Have you verified it truly is? If Thunderbird uses some other server, that would explain why sending from Roundcube works but from Thunderbird not.
I found the problem. The options for smtp over ssl were disabled. I enabled them, and now it works: Code: smtp inet n - n - - smtpd #smtp inet n - n - 1 postscreen #smtpd pass - - n - - smtpd #dnsblog unix - - n - 0 dnsblog #tlsproxy unix - - n - 0 tlsproxy submission inet n - n - - smtpd # -o syslog_name=postfix/submission # -o smtpd_tls_security_level=encrypt -o smtpd_sasl_auth_enable=yes # -o smtpd_reject_unlisted_recipient=no # -o smtpd_client_restrictions=$mua_client_restrictions # -o smtpd_helo_restrictions=$mua_helo_restrictions # -o smtpd_sender_restrictions=$mua_sender_restrictions # -o smtpd_recipient_restrictions=permit_sasl_authenticated,reject # -o milter_macro_daemon_name=ORIGINATING smtps inet n - n - - smtpd # -o syslog_name=postfix/smtps -o smtpd_tls_wrappermode=yes -o smtpd_sasl_auth_enable=yes # -o smtpd_reject_unlisted_recipient=no # -o smtpd_client_restrictions=$mua_client_restrictions # -o smtpd_helo_restrictions=$mua_helo_restrictions # -o smtpd_sender_restrictions=$mua_sender_restrictions # -o smtpd_recipient_restrictions=permit_sasl_authenticated,reject # -o milter_macro_daemon_name=ORIGINATING # The lines Code: -o smtpd_sasl_auth_enable=yes -o smtpd_tls_wrappermode=yes -o smtpd_sasl_auth_enable=yes had originally been commented out. Since I did that change, SMTP works. However, I would also like to just follow your suggestion, to be sure. How can I not be sure that Thunderbird uses my domain for smtp? Is there another place where the smtp server is set, besides the one in the account configuration? I have several smtp servers configured there, but I'm sure for the email account in question I was using only my domain, as far as can be set by me (according to my knowledge). And one more question: would it be wise to also enable any other of the options? I wonder particularly about Code: # -o smtpd_tls_security_level=encrypt
Use the settings in the tutorial, and check you really have done that. Thunderbird has in account settings the sent mail server.
I'm not sure which tutorial you are referring to. I found nothing specific in the installation tutorial for CentOS 7.
