No content - sent mail

from one second to the other no content is sent. In the text area of the recipient it says “no Content”. If I display the source code, it also shows “no content” - both for the recipient and in the emClient (sent mails) neither under PlainText nor under html.

Mac emClient 8.1.1083 (c197f89)
System OSX 10.11.6

I have an Exchange account and an IMAP account. Deleted both accounts and recreated them after a reboot. The speed has not changed, also no updates have run. No errors are shown under sync operations. Older mails are normal and have content.

It looks like when recreating the content is just forgotten.

What else can I do?

There are a few entries here, they are older and I did not find a solution there.
regards - Hans