calendar invitation message reject as UNDELIVERABLE due InvalidCharsetException, Character set name (RCMAIL+AF8-CHARSET), roundcuebe 1.3.x

[pafcioooo]

While creating event in calendar with attendee email after event is send the remote sender answers with undeliverable status.

Sample rejected message info:
Delivery has failed to these recipients or groups:
------@-------.mail.onmicrosoft.com
The email system had a problem processing this message. It won't try to deliver this message again.
Diagnostic information for administrators:
Generating server: --------------------------

------@-------.mail.onmicrosoft.com
Remote Server returned '550 5.6.0 CAT.InvalidContent.Exception: InvalidCharsetException, Character set name (RCMAIL+AF8-CHARSET) is invalid or not installed.; cannot handle content of message with InternalId 107335527701685, InternetMessageId b2c0c700008585c1c0422b4ae111de9a@indevops.com.'

Original message headers:

[pafcioooo]

@fasterit any ideas how to troubleshoot this?

[fasterit]

Sounds like a broken Header.
Send to a mail server where you can receive the full header to inspect and / or dump the sendmail input to a file by replacing the sendmail binary.