Sorry, re-read your question and realise my suggestion would only help you get SASL authentication working. > On 31 Mar 2021, at 09:19, Jamie Burchell <mail at jamieburchell.com> wrote: > > I'm pretty sure I encountered this and needed to yum install cyrus-sasl-plain to resolve it. > >> On 29 Mar 2021, at 20:31, Nicolas Kovacs <info at microlinux.fr> wrote: >> >> Hi, >> >> My main mail server is running CentOS 7 with Postfix and Dovecot. >> >> Last week I was surprised to see that Postfix had some troubles on this >> machine, according to Icinga. I took a peek at the logs: >> >> # journalctl -p err >> Mar 28 04:37:02 sd-151768 postfix/smtpd[2786]: fatal: no SASL authentication >> mechanisms >> Mar 28 04:37:02 sd-151768 postfix/smtpd[2788]: fatal: no SASL authentication >> mechanisms >> Mar 28 04:37:02 sd-151768 postfix/smtpd[2790]: fatal: no SASL authentication >> mechanisms >> Mar 28 04:37:02 sd-151768 postfix/smtpd[2792]: fatal: no SASL authentication >> mechanisms >> Mar 28 04:37:02 sd-151768 postfix/smtpd[2794]: fatal: no SASL authentication >> mechanisms >> ... >> >> And in /var/log/maillog I found a tsunami of these: >> >> Mar 28 03:18:33 sd-151768 postfix/smtpd[29589]: warning: >> unknown[45.227.253.115]: SASL LOGIN authentication failed: UGFzc3dvcmQ6 >> Mar 28 03:18:33 sd-151768 postfix/smtpd[29589]: lost connection after AUTH from >> unknown[45.227.253.115] >> Mar 28 03:18:33 sd-151768 postfix/smtpd[29589]: disconnect from >> unknown[45.227.253.115] >> >> My first reaction was to manually ban the IP addresses / networks which caused >> the flood, using my firewall: >> >> # firewall-cmd --permanent --add-rich-rule="rule family='ipv4' source >> address='45.227.253.0/24' reject" >> # firewall-cmd --reload >> >> I'm already using fail2ban in conjunction with firewalld to prevent brute force >> SSH attacks. >> >> Q: can I use it in a similar configuration to stop Postfix from getting flooded >> and brought down to its knees? >> >> Thanks & cheers from the sunny South of France, >> >> Niki >> >> -- >> Microlinux - Solutions informatiques durables >> 7, place de l'église - 30730 Montpezat >> Site : https://www.microlinux.fr >> Blog : https://blog.microlinux.fr >> Mail : info at microlinux.fr >> Tél. : 04 66 63 10 32 >> Mob. : 06 51 80 12 12 >> _______________________________________________ >> CentOS mailing list >> CentOS at centos.org >> https://lists.centos.org/mailman/listinfo/centos