Outlook 365 for Mac - not sending attachments

This issue also happens with Office 365 on a corporate account... I work for an university and all employees and students work with Office 365 (or MS 365 as it seems to be called now?). I recently returned from holiday so I can't tell for sure when or with what Outlook version this issue with losing attachments started to occur. I'm currently working with Outlook version 16.64 (22082100) which I installed via the Mac App Store. It was updated about 2 weeks ago. My Mac runs Monterey 12.5.1. On all occasions I can see the mail including the attachment in my sent items folder in Outlook or the web interface. But a lot of recipients complain the attachment is not included when they receive my mail. These are mostly colleagues that are part of the same organization in Office 365.

So it doesn't only occur with Google mail services, also with Microsofts very own Office 365 this problem occurs.

After reading here that switching back to the old layout of Outlook seems to fix this issue, I also switched back. I held back this switch for quite a while since a few basic features such as S/MIME signing (and encrypting) mail with the new Outlook wasn't possible for a long, long time. I've been a Office user for a long time and have seen various versions of Outlook for Mac throughout the years, but something as basic as attachments getting dropped along the way is a new all time low for me...

I've been having this issue for weeks. Files will show as attached when drafting a message, will show as attached even when pressing send, and then when I check my sent folder it turns out the file was not attached. Not sure if this is Mac related, or because I'm using a Gmail based account.

Same here. Intermittent issue with attachments which are visibly attached before hitting send not actually being sent and not showing up as attachments in the same email once it is in the sent folder. This doesn't seem to happen when I shelve the attachments in Dropzone and then attach from there.

This is a huge issue when sending time sensitive legal documents!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I'm also experiencing this issue with multiple users in our org, not all of them though. They're all running most recent macOS (12.5.1) with most recent Outlook (16.64). For the affected users, downgrading to 16.62 has fixed the issue. You can download that version here: https://officecdnmac.microsoft.com/pr/C1297A47-86C4-4C1F-97FA-950631F94777/MacAutoupdate/Microsoft_Outlook_16.62.22061100_Installer.pkg, thanks to homebrew-cask for keeping a version history :)

@Microsoft: this issue is unacceptable. This behaviour is *very* misleading for users as it silently fails to add the attachments and doesn't even display an error. Please fix this as soon as possible, I don't like being stuck on an older version...

Same issue here. 2021 MacBook Pro, Monterey v12.5.1, Outlook for Mac 16.4

I believe I updated to the newest Monterey sometime during this problem, which has been going on for about 6 weeks now (mid-July?).

I was starting to think I was getting really absent-minded because of the number of clients that would email back and say "no attachment, can you re-send?" The problem is periodic and seems to have no rhyme or reason, although it is increasingly frequent these days.. I can re-send the same email with the attachment re-attached and it might go through one time and might not another time. I can start a new email and attach the item and it may or may not go through. (As the OP mentioned, the original email shows up as sent, but without the attachment even though I triple-checked to make sure it was there before I hit send.) The type of document and whether I drag/drop the attachment or use the "attach" tool to select the document doesn't seem to make any difference. The suggested diagnostic step of going into safe mode and trying to send an email with an attachment would be great IF none of my attachments ever went through, but some do and some don't. I'd have to send 100 over the course of a day to see if all 100 went through or not.