Hello,
we have a problem with our clients of Outlook for mac 2016. Maybe other have the same problems currently?
Everytime a user will change a meeting and will sent the update mail to the participants, the mails remain in the outbox.
Sometimes other, simple mails also fail and we aren't reach the sice limit of the mail/attachments.
The error we only get is "unknown error from outlook"
The o365 outlook for mac version is the newest out there, so up to date.
We use an onpremise exchange 2010 server.