Sending is blocked, slow, or shows an add-in error

If Outlook shows a message such as "an add-in is taking longer than expected" when you send, delays the send, or shows an add-in error on send, the cause is almost always the same: Outlook is running an older, cached copy of the add-in.

Outlook keeps a local copy of add-ins so they load quickly. When a newer version is released, Outlook can keep using the cached older copy until that cache is cleared. Clearing it makes Outlook load the current version, which resolves this.

The fix

1. First, close Outlook completely and reopen it. That alone often pulls the current version.
2. If it still happens, clear the add-in cache for your Outlook client. This is the reliable fix.

Why a restart alone might not be enough

For add-ins deployed centrally by an administrator, Microsoft can take up to 72 hours to roll an updated version out to every user. During that window, a restart may still load the older cached copy. Clearing the cache manually skips the wait and loads the current version immediately.

Confirming it's fixed

After clearing the cache, open the MailTail pane and check the version number at the bottom. If it matches the current version we've given you, you're on the latest build and sending should behave normally. If it's still happening after that, email support@mailtail.io with your Outlook client and version number.