The "You are spamming" response of comment 59 to "RCPT TO" is probably just due to my ISP's IP address range being on a blacklist. After further testing using openssl command line method, it appears that the SMTPUTF8 parameter on the "MAIL TO" command sent by TB *is* causing the problem with "Sorry, this is spam" response after sending the DATA (see bug 1710224 comment 67). However, sending this should be OK and causes no problems for other servers that also support SMTPUTF8 like gmail and courier (Allessandro's tana.it). Why "Easyname" smtp server is seeing the message as spam when the SMTPUTF8 parameter is present in the "MAIL TO" command is not yet known but seems to be a server bug.
Bug 1563891 Comment 60 Edit History
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The "You are spamming" response of comment 59 to "RCPT TO" is probably just due to my ISP's IP address range being on a blacklist. After further testing using openssl command line method, it appears that the SMTPUTF8 parameter on the "MAIL TO" command sent by TB *is* causing the problem with "Sorry, this is spam" response after sending the DATA (see bug 1710224 comment 67). However, sending this should be OK and causes no problems for other servers that also support SMTPUTF8 like gmail and courier (Alessandro's tana.it). Why "Easyname" smtp server is seeing the message as spam when the SMTPUTF8 parameter is present in the "MAIL TO" command is not yet known but seems to be a server bug.