I know this is one of those intermittent issues that engineers just hate, but the subject says it.

We have a team set up on BitBucket, all contributing to a repo that has a post-commit hook that sends an email diff. The email address for the email diffs is a group alias that our team has used for years. So it's always emailing the same address.

Sometimes the emails come through, and sometimes they don't. It doesn't seem to be associated with any particular user.