At a tinderbox image 17_1_systemd-20200720-185100 I got # ls | mail -s test tinderbox@zwiebeltoralf.de send-mail: Invalid response SMTP server Can't send mail: sendmail process failed with error code 1 whereas re-emerging it with "-gnutls" works fine. ================================================================= Package Settings ================================================================= mail-mta/ssmtp-2.64-r3::gentoo was built with the following: USE="ipv6 mta ssl -gnutls -libressl" ABI_X86="(64)"