diff --git a/examples/inventory_corporate.html b/examples/inventory_corporate.html
index 67ad386..1c43870 100644
--- a/examples/inventory_corporate.html
+++ b/examples/inventory_corporate.html
@@ -612,7 +612,7 @@ input.invalid, select.invalid, textarea.invalid {
 
 <div class="actions">
   <button type="button" class="btn btn-primary" onclick="exportCSV()">📥 Exporteer CSV</button>
-  <button type="button" class="btn btn-success" onclick="sendEmail()">📧 Verstuur per Email</button>
+  <button type="button" class="btn btn-success" onclick="sendEmail(this)">📧 Verstuur per Email</button>
   <button type="button" class="btn btn-danger" onclick="clearForm()">🗑️ Formulier Wissen</button>
 </div>
 
@@ -980,50 +980,67 @@ input.invalid, select.invalid, textarea.invalid {
     };
     
     // Send email
-    window.sendEmail = function() {
+    window.sendEmail = function(btn) {
         if (!validateAll()) {
             showToast('Vul eerst alle verplichte velden in', 'error');
             return;
         }
         
-        const data = getFormData();
-        
-        // Build subject
-        let subject = CONFIG.export.mailto.subject_prefix;
-        if (CONFIG.export.mailto.include_timestamp) {
-            subject += ' - ' + formatDateTime(new Date());
+        // Show loading state immediately
+        const button = btn || document.querySelector('[onclick*="sendEmail"]');
+        const originalText = button ? button.innerHTML : '';
+        if (button) {
+            button.innerHTML = '⏳ Email voorbereiden...';
+            button.disabled = true;
         }
-        CONFIG.export.mailto.subject_fields.forEach(fieldId => {
-            if (data[fieldId]) {
-                subject += ' - ' + data[fieldId];
-            }
-        });
-        
-        // Build body
-        let body = 'INVENTARISATIE GEGEVENS\n';
-        body += '========================\n\n';
-        body += 'Formulier: ' + CONFIG.name + '\n';
-        body += 'Versie: ' + CONFIG.version + '\n';
-        body += 'Datum: ' + formatDateTime(new Date()) + '\n\n';
         
-        Object.entries(data).forEach(([key, value]) => {
-            if (value && value !== '' && !key.includes('foto') && !key.includes('photo')) {
-                const label = document.querySelector(`label[for="${key}"]`);
-                const labelText = label ? label.textContent.replace('*', '').trim() : key;
-                const displayValue = Array.isArray(value) ? value.join(', ') : value;
-                body += labelText + ': ' + displayValue + '\n';
+        // Use setTimeout to allow UI to update before heavy processing
+        setTimeout(function() {
+            const data = getFormData();
+            
+            // Build subject
+            let subject = CONFIG.export.mailto.subject_prefix;
+            if (CONFIG.export.mailto.include_timestamp) {
+                subject += ' - ' + formatDateTime(new Date());
             }
-        });
-        
-        body += '\n========================\n';
-        body += 'Let op: Foto\'s kunnen niet via mailto worden verzonden.\n';
-        body += 'Gebruik CSV export voor complete data inclusief foto\'s.';
-        
-        const mailto = 'mailto:' + encodeURIComponent(CONFIG.export.mailto.to) +
-            '?subject=' + encodeURIComponent(subject) +
-            '&body=' + encodeURIComponent(body);
-        
-        window.location.href = mailto;
+            CONFIG.export.mailto.subject_fields.forEach(fieldId => {
+                if (data[fieldId]) {
+                    subject += ' - ' + data[fieldId];
+                }
+            });
+            
+            // Build body
+            let body = 'INVENTARISATIE GEGEVENS\n';
+            body += '========================\n\n';
+            body += 'Formulier: ' + CONFIG.name + '\n';
+            body += 'Versie: ' + CONFIG.version + '\n';
+            body += 'Datum: ' + formatDateTime(new Date()) + '\n\n';
+            
+            Object.entries(data).forEach(([key, value]) => {
+                if (value && value !== '' && !key.includes('foto') && !key.includes('photo')) {
+                    const label = document.querySelector(`label[for="${key}"]`);
+                    const labelText = label ? label.textContent.replace('*', '').trim() : key;
+                    const displayValue = Array.isArray(value) ? value.join(', ') : value;
+                    body += labelText + ': ' + displayValue + '\n';
+                }
+            });
+            
+            body += '\n========================\n';
+            body += 'Let op: Foto\'s kunnen niet via mailto worden verzonden.\n';
+            body += 'Gebruik CSV export voor complete data inclusief foto\'s.';
+            
+            const mailto = 'mailto:' + encodeURIComponent(CONFIG.export.mailto.to) +
+                '?subject=' + encodeURIComponent(subject) +
+                '&body=' + encodeURIComponent(body);
+            
+            // Restore button state
+            if (button) {
+                button.innerHTML = originalText;
+                button.disabled = false;
+            }
+            
+            window.location.href = mailto;
+        }, 50);
     };
     
     // Clear form
diff --git a/examples/inventory_minimal.html b/examples/inventory_minimal.html
index fce1a92..cdd62e2 100644
--- a/examples/inventory_minimal.html
+++ b/examples/inventory_minimal.html
@@ -643,7 +643,7 @@ select {
 
 <div class="actions">
   <button type="button" class="btn btn-primary" onclick="exportCSV()">📥 Exporteer CSV</button>
-  <button type="button" class="btn btn-success" onclick="sendEmail()">📧 Verstuur per Email</button>
+  <button type="button" class="btn btn-success" onclick="sendEmail(this)">📧 Verstuur per Email</button>
   <button type="button" class="btn btn-danger" onclick="clearForm()">🗑️ Formulier Wissen</button>
 </div>
 
@@ -1011,50 +1011,67 @@ select {
     };
     
     // Send email
-    window.sendEmail = function() {
+    window.sendEmail = function(btn) {
         if (!validateAll()) {
             showToast('Vul eerst alle verplichte velden in', 'error');
             return;
         }
         
-        const data = getFormData();
-        
-        // Build subject
-        let subject = CONFIG.export.mailto.subject_prefix;
-        if (CONFIG.export.mailto.include_timestamp) {
-            subject += ' - ' + formatDateTime(new Date());
+        // Show loading state immediately
+        const button = btn || document.querySelector('[onclick*="sendEmail"]');
+        const originalText = button ? button.innerHTML : '';
+        if (button) {
+            button.innerHTML = '⏳ Email voorbereiden...';
+            button.disabled = true;
         }
-        CONFIG.export.mailto.subject_fields.forEach(fieldId => {
-            if (data[fieldId]) {
-                subject += ' - ' + data[fieldId];
-            }
-        });
-        
-        // Build body
-        let body = 'INVENTARISATIE GEGEVENS\n';
-        body += '========================\n\n';
-        body += 'Formulier: ' + CONFIG.name + '\n';
-        body += 'Versie: ' + CONFIG.version + '\n';
-        body += 'Datum: ' + formatDateTime(new Date()) + '\n\n';
         
-        Object.entries(data).forEach(([key, value]) => {
-            if (value && value !== '' && !key.includes('foto') && !key.includes('photo')) {
-                const label = document.querySelector(`label[for="${key}"]`);
-                const labelText = label ? label.textContent.replace('*', '').trim() : key;
-                const displayValue = Array.isArray(value) ? value.join(', ') : value;
-                body += labelText + ': ' + displayValue + '\n';
+        // Use setTimeout to allow UI to update before heavy processing
+        setTimeout(function() {
+            const data = getFormData();
+            
+            // Build subject
+            let subject = CONFIG.export.mailto.subject_prefix;
+            if (CONFIG.export.mailto.include_timestamp) {
+                subject += ' - ' + formatDateTime(new Date());
             }
-        });
-        
-        body += '\n========================\n';
-        body += 'Let op: Foto\'s kunnen niet via mailto worden verzonden.\n';
-        body += 'Gebruik CSV export voor complete data inclusief foto\'s.';
-        
-        const mailto = 'mailto:' + encodeURIComponent(CONFIG.export.mailto.to) +
-            '?subject=' + encodeURIComponent(subject) +
-            '&body=' + encodeURIComponent(body);
-        
-        window.location.href = mailto;
+            CONFIG.export.mailto.subject_fields.forEach(fieldId => {
+                if (data[fieldId]) {
+                    subject += ' - ' + data[fieldId];
+                }
+            });
+            
+            // Build body
+            let body = 'INVENTARISATIE GEGEVENS\n';
+            body += '========================\n\n';
+            body += 'Formulier: ' + CONFIG.name + '\n';
+            body += 'Versie: ' + CONFIG.version + '\n';
+            body += 'Datum: ' + formatDateTime(new Date()) + '\n\n';
+            
+            Object.entries(data).forEach(([key, value]) => {
+                if (value && value !== '' && !key.includes('foto') && !key.includes('photo')) {
+                    const label = document.querySelector(`label[for="${key}"]`);
+                    const labelText = label ? label.textContent.replace('*', '').trim() : key;
+                    const displayValue = Array.isArray(value) ? value.join(', ') : value;
+                    body += labelText + ': ' + displayValue + '\n';
+                }
+            });
+            
+            body += '\n========================\n';
+            body += 'Let op: Foto\'s kunnen niet via mailto worden verzonden.\n';
+            body += 'Gebruik CSV export voor complete data inclusief foto\'s.';
+            
+            const mailto = 'mailto:' + encodeURIComponent(CONFIG.export.mailto.to) +
+                '?subject=' + encodeURIComponent(subject) +
+                '&body=' + encodeURIComponent(body);
+            
+            // Restore button state
+            if (button) {
+                button.innerHTML = originalText;
+                button.disabled = false;
+            }
+            
+            window.location.href = mailto;
+        }, 50);
     };
     
     // Clear form
diff --git a/examples/inventory_modern.html b/examples/inventory_modern.html
index 6abc3c1..ac1c776 100644
--- a/examples/inventory_modern.html
+++ b/examples/inventory_modern.html
@@ -674,7 +674,7 @@ input.invalid, select.invalid, textarea.invalid {
 
 <div class="actions">
   <button type="button" class="btn btn-primary" onclick="exportCSV()">📥 Exporteer CSV</button>
-  <button type="button" class="btn btn-success" onclick="sendEmail()">📧 Verstuur per Email</button>
+  <button type="button" class="btn btn-success" onclick="sendEmail(this)">📧 Verstuur per Email</button>
   <button type="button" class="btn btn-danger" onclick="clearForm()">🗑️ Formulier Wissen</button>
 </div>
 
@@ -1042,50 +1042,67 @@ input.invalid, select.invalid, textarea.invalid {
     };
     
     // Send email
-    window.sendEmail = function() {
+    window.sendEmail = function(btn) {
         if (!validateAll()) {
             showToast('Vul eerst alle verplichte velden in', 'error');
             return;
         }
         
-        const data = getFormData();
-        
-        // Build subject
-        let subject = CONFIG.export.mailto.subject_prefix;
-        if (CONFIG.export.mailto.include_timestamp) {
-            subject += ' - ' + formatDateTime(new Date());
+        // Show loading state immediately
+        const button = btn || document.querySelector('[onclick*="sendEmail"]');
+        const originalText = button ? button.innerHTML : '';
+        if (button) {
+            button.innerHTML = '⏳ Email voorbereiden...';
+            button.disabled = true;
         }
-        CONFIG.export.mailto.subject_fields.forEach(fieldId => {
-            if (data[fieldId]) {
-                subject += ' - ' + data[fieldId];
-            }
-        });
-        
-        // Build body
-        let body = 'INVENTARISATIE GEGEVENS\n';
-        body += '========================\n\n';
-        body += 'Formulier: ' + CONFIG.name + '\n';
-        body += 'Versie: ' + CONFIG.version + '\n';
-        body += 'Datum: ' + formatDateTime(new Date()) + '\n\n';
         
-        Object.entries(data).forEach(([key, value]) => {
-            if (value && value !== '' && !key.includes('foto') && !key.includes('photo')) {
-                const label = document.querySelector(`label[for="${key}"]`);
-                const labelText = label ? label.textContent.replace('*', '').trim() : key;
-                const displayValue = Array.isArray(value) ? value.join(', ') : value;
-                body += labelText + ': ' + displayValue + '\n';
+        // Use setTimeout to allow UI to update before heavy processing
+        setTimeout(function() {
+            const data = getFormData();
+            
+            // Build subject
+            let subject = CONFIG.export.mailto.subject_prefix;
+            if (CONFIG.export.mailto.include_timestamp) {
+                subject += ' - ' + formatDateTime(new Date());
             }
-        });
-        
-        body += '\n========================\n';
-        body += 'Let op: Foto\'s kunnen niet via mailto worden verzonden.\n';
-        body += 'Gebruik CSV export voor complete data inclusief foto\'s.';
-        
-        const mailto = 'mailto:' + encodeURIComponent(CONFIG.export.mailto.to) +
-            '?subject=' + encodeURIComponent(subject) +
-            '&body=' + encodeURIComponent(body);
-        
-        window.location.href = mailto;
+            CONFIG.export.mailto.subject_fields.forEach(fieldId => {
+                if (data[fieldId]) {
+                    subject += ' - ' + data[fieldId];
+                }
+            });
+            
+            // Build body
+            let body = 'INVENTARISATIE GEGEVENS\n';
+            body += '========================\n\n';
+            body += 'Formulier: ' + CONFIG.name + '\n';
+            body += 'Versie: ' + CONFIG.version + '\n';
+            body += 'Datum: ' + formatDateTime(new Date()) + '\n\n';
+            
+            Object.entries(data).forEach(([key, value]) => {
+                if (value && value !== '' && !key.includes('foto') && !key.includes('photo')) {
+                    const label = document.querySelector(`label[for="${key}"]`);
+                    const labelText = label ? label.textContent.replace('*', '').trim() : key;
+                    const displayValue = Array.isArray(value) ? value.join(', ') : value;
+                    body += labelText + ': ' + displayValue + '\n';
+                }
+            });
+            
+            body += '\n========================\n';
+            body += 'Let op: Foto\'s kunnen niet via mailto worden verzonden.\n';
+            body += 'Gebruik CSV export voor complete data inclusief foto\'s.';
+            
+            const mailto = 'mailto:' + encodeURIComponent(CONFIG.export.mailto.to) +
+                '?subject=' + encodeURIComponent(subject) +
+                '&body=' + encodeURIComponent(body);
+            
+            // Restore button state
+            if (button) {
+                button.innerHTML = originalText;
+                button.disabled = false;
+            }
+            
+            window.location.href = mailto;
+        }, 50);
     };
     
     // Clear form
diff --git a/src/generator.py b/src/generator.py
index 426aa1b..964bfc7 100644
--- a/src/generator.py
+++ b/src/generator.py
@@ -153,7 +153,7 @@ def generate_html(config: InventoryConfig) -> str:
     if config.export.csv.enabled:
         actions_html += '  <button type="button" class="btn btn-primary" onclick="exportCSV()">📥 Exporteer CSV</button>\n'
     if config.export.mailto.enabled:
-        actions_html += '  <button type="button" class="btn btn-success" onclick="sendEmail()">📧 Verstuur per Email</button>\n'
+        actions_html += '  <button type="button" class="btn btn-success" onclick="sendEmail(this)">📧 Verstuur per Email</button>\n'
     actions_html += '  <button type="button" class="btn btn-danger" onclick="clearForm()">🗑️ Formulier Wissen</button>\n'
     actions_html += '</div>\n'
     
diff --git a/src/templates.py b/src/templates.py
index 2eb5ecd..13f2e67 100644
--- a/src/templates.py
+++ b/src/templates.py
@@ -1291,50 +1291,67 @@ JAVASCRIPT = """
     };
     
     // Send email
-    window.sendEmail = function() {
+    window.sendEmail = function(btn) {
         if (!validateAll()) {
             showToast('Vul eerst alle verplichte velden in', 'error');
             return;
         }
         
-        const data = getFormData();
-        
-        // Build subject
-        let subject = CONFIG.export.mailto.subject_prefix;
-        if (CONFIG.export.mailto.include_timestamp) {
-            subject += ' - ' + formatDateTime(new Date());
+        // Show loading state immediately
+        const button = btn || document.querySelector('[onclick*="sendEmail"]');
+        const originalText = button ? button.innerHTML : '';
+        if (button) {
+            button.innerHTML = '⏳ Email voorbereiden...';
+            button.disabled = true;
         }
-        CONFIG.export.mailto.subject_fields.forEach(fieldId => {
-            if (data[fieldId]) {
-                subject += ' - ' + data[fieldId];
-            }
-        });
-        
-        // Build body
-        let body = 'INVENTARISATIE GEGEVENS\\n';
-        body += '========================\\n\\n';
-        body += 'Formulier: ' + CONFIG.name + '\\n';
-        body += 'Versie: ' + CONFIG.version + '\\n';
-        body += 'Datum: ' + formatDateTime(new Date()) + '\\n\\n';
         
-        Object.entries(data).forEach(([key, value]) => {
-            if (value && value !== '' && !key.includes('foto') && !key.includes('photo')) {
-                const label = document.querySelector(`label[for="${key}"]`);
-                const labelText = label ? label.textContent.replace('*', '').trim() : key;
-                const displayValue = Array.isArray(value) ? value.join(', ') : value;
-                body += labelText + ': ' + displayValue + '\\n';
+        // Use setTimeout to allow UI to update before heavy processing
+        setTimeout(function() {
+            const data = getFormData();
+            
+            // Build subject
+            let subject = CONFIG.export.mailto.subject_prefix;
+            if (CONFIG.export.mailto.include_timestamp) {
+                subject += ' - ' + formatDateTime(new Date());
             }
-        });
-        
-        body += '\\n========================\\n';
-        body += 'Let op: Foto\\'s kunnen niet via mailto worden verzonden.\\n';
-        body += 'Gebruik CSV export voor complete data inclusief foto\\'s.';
-        
-        const mailto = 'mailto:' + encodeURIComponent(CONFIG.export.mailto.to) +
-            '?subject=' + encodeURIComponent(subject) +
-            '&body=' + encodeURIComponent(body);
-        
-        window.location.href = mailto;
+            CONFIG.export.mailto.subject_fields.forEach(fieldId => {
+                if (data[fieldId]) {
+                    subject += ' - ' + data[fieldId];
+                }
+            });
+            
+            // Build body
+            let body = 'INVENTARISATIE GEGEVENS\\n';
+            body += '========================\\n\\n';
+            body += 'Formulier: ' + CONFIG.name + '\\n';
+            body += 'Versie: ' + CONFIG.version + '\\n';
+            body += 'Datum: ' + formatDateTime(new Date()) + '\\n\\n';
+            
+            Object.entries(data).forEach(([key, value]) => {
+                if (value && value !== '' && !key.includes('foto') && !key.includes('photo')) {
+                    const label = document.querySelector(`label[for="${key}"]`);
+                    const labelText = label ? label.textContent.replace('*', '').trim() : key;
+                    const displayValue = Array.isArray(value) ? value.join(', ') : value;
+                    body += labelText + ': ' + displayValue + '\\n';
+                }
+            });
+            
+            body += '\\n========================\\n';
+            body += 'Let op: Foto\\'s kunnen niet via mailto worden verzonden.\\n';
+            body += 'Gebruik CSV export voor complete data inclusief foto\\'s.';
+            
+            const mailto = 'mailto:' + encodeURIComponent(CONFIG.export.mailto.to) +
+                '?subject=' + encodeURIComponent(subject) +
+                '&body=' + encodeURIComponent(body);
+            
+            // Restore button state
+            if (button) {
+                button.innerHTML = originalText;
+                button.disabled = false;
+            }
+            
+            window.location.href = mailto;
+        }, 50);
     };
     
     // Clear form