The most reliable fix is to use a hosted Add to Calendar service like AddEvent rather than raw URL links or .ics file attachments. Here is why links fail and how to resolve each issue.

Why Add to Calendar links break in email clients

Outlook desktop wraps links Outlook wraps all links in its own safe-link redirect URL (safelinks.protection.outlook.com). This can break calendar deep-links that rely on specific URL formats. AddEvent links are designed to survive this wrapping - they redirect correctly from Outlook's safe-links proxy.

Gmail clips long emails Gmail clips emails over ~102KB, which can cut off links near the bottom of the message. Keep your email lean and place the Add to Calendar link high in the content.

In-app browsers Recipients who open emails in the Gmail app or Outlook mobile app are in a sandboxed browser with limited calendar access. The Add to Calendar flow may not complete. Direct them to open in Safari or Chrome where possible.

Plain .ics attachments .ics files behave inconsistently across email clients - some render a native "Add to Calendar" prompt, others just download a file that recipients do not know how to open. Add to Calendar links are more reliable because they open a guided flow in the browser.

The most reliable approach

• Work across Gmail, Outlook, Apple Mail, and mobile email apps
• Handle Outlook safelinks wrapping correctly
• Guide each recipient to choose their calendar app
• Can be updated after sending if event details change