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« Last post by knonem on May 05, 2021, 09:09:04 pm »
Hi,
after setting up S/MIME on my account a couple of weeks ago, today I tried to send an unencrypted e-mail, which was rejected by the SMTP-Server of my e-Mail provider (1&1 IONOS SE).
After asking I got the following explanation from my provider:
"Your e-Mail was rejected by our SMTP-Server, because it does not comply with the defined standards in RFC5321 and RFC5322.
Please make sure, that the e-Mail client fulfills the following criteria when sending an e-Mail:
1. The e-Mail header must have a valid 'date'-field according to RFC2822: (Link to IETF RFC2822, Section 3.3 -> I'm not allowed to post links)
2. The following field may be present only once: "Date:", "From:", "Sender:", "To:", "CC:", "BCC:", "Subject:"
3. If the field types named above are used, they may not be empty and must be syntactically correct.
Note: The field types „To:“, „CC:“ and „BCC:“ can of course contain several recipients.
We stick to the recommendations out of RFC7103 and to not auto-correct faulty messages, because this will make DKIM-signatures invalid."
I tried several recipients and always got the same error when trying to send an unencrypted e-Mail. When sending an S/MIME encrypted e-Mail however, it was sent correctly.
Can you look into this?
Thanks
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