Apple Mail cannot connect to an outgoing mail server when forwarding an email as an attachment. This does not happen with most emails; just those where another email as been included as an attachment. It is not specific to the email account or its host (i.e. it happens with all email accounts hosted by different services).
MacBook Pro 14″, macOS 15.5
Re: "Apple Mail Forwarding Issue :
Mail cannot connect to an outgoing mail server when forwarding an email as an attachment".
It may be that an email file format is not suitable for the forwarding method you use.
(Eg: Emails export and import from Mail as .mbox format files.)
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Re: " It is not specific to the email account or its host
(i.e. it happens with all email accounts hosted by different services)".
Seems forwarding an email, and sending an attachment may be two very separate Mail actions.
If you are looking for suggestions:
Try Apple's suggested method for forwarding emals in MacOS Sequoia:
Reply to, forward, or follow up on emails in Mail on Mac - Apple Support
ie: Click to forward the email, and add your own text at the top of the message it appears in.
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Else if you really want to send an email as an attachment.
You can export the email (eg: as a .pdf file: (select the message in sidebar > click File > Export as .pdf)
Attach to email as usual.
Apple Mail Forwarding Issue
