Email attachments in Outlook 2016 convert to an "ATT" file name followed by a number sequence (version1606.7070.20136 or later)

Last updated: September 2016


Your email attachments might get deleted after you send your email, and the filename appears to the recipients as ATT<XXXXXX>, where <XXXXXX> is an arbitrary number sequence. This happens if you have added a digital signature to your message, but turn it off when sending your email.

Status: Investigating

Our engineering team is working on a fix and will update this page when a fix or workaround becomes available.

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See Also

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