I just setup someone with a Usermin acct to be able to use the readmail/webmail feature only. Incoming mail works just fine, but their outgoing mail never got to the recipient (tested sending to myself). /var/log/maillog shows (sensitive information CHANGED) : from=USEREMAIL@DOMAIN.com, size=558, class=0, nrcpts=1, msgid=1532704772.30975@DOMAIN.com, relay=USER@localhost to=ME@DOMAIN.com, ctladdr=USEREMAIL@DOMAIN.com (532/509), delay=00:00:01, xdelay=00:00:01, mailer=relay, pri=30558, relay=[127.0.0.1]...