The SMTP response "Line too long" occurs when you have > 998 continuous characters in the e-mail message body.  A hard return (CR LF) is required in the message body prior to exceeding that 998 character limit.

I've seen this happen with Multi-Part MIME-format messages with an attachment.  Are you forwarding as Normal, Text, or Embed as Attachment? The Embed as Attachment forwarding can get wonky when the email already has an attachment embedded.

Hi Scarab,

thank you for this detailed Information. There's no attachment but a lot of text in the mail. I don't know if there's a hard return (CR LF). I'm always using 'Enter' and not 'Shift' + 'Enter' to do a CR. But could it be that a mail client is changing the way the return is made? I'm only working with the web UI of SmarterMail. So forwarding or answering mail is done as Normal. But I think my mail partner is using his smartphone or another fat mail client software.

I tried to send the mail once more yesterday by copying my last two messages and this worked fine.

Kind Regards

TheExpert

Hi all,

this issue is still not fixed. Even with SmarterMail 16.3.6855 there are line too long errors. There's a hint for fixing this issue with the newest release: "Fixed: Certain Base64 encoded message parts are not getting RFC line breaks causing 550 Line too long Errors."

I believe that it is caused by emoticons that are not written as letters, i. e. ;-). If they are shown as signs in the mail text and you are answering or forwarding the mail the SMTP error "line too long" will happen.

Kind Regrads