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