I began getting these errors about 3 months ago:
1.) This is an SMTP protocol error log for virtual server ID 1, connection #xxx. The remote host "xx.xx.xx.xx", responded to the SMTP command "xexch50" with "504 Need to authenticate first ". The full command sent was "XEXCH50 1836 2 ". This will probably cause the connection to fail.
2.) This is an SMTP protocol log for virtual server ID 1, connection #169. The client at "xx.xx.xx.xx" sent a "xexch50" command, and the SMTP server responded with "504 Need to authenticate first ". The full command sent was "xexch50 2188 2". This will probably cause the connection to fail.
We are NOT losing any mail.
I DO have close to 4000 botnet subnets blocked in SMTP Virtual Server properties (Properties->Access->Connection Control->Connection->All except the list below, but I have had that [growing] list for many months before these events began getting logged. I get about 50-60 of these on weekends and up to 200 on weekdays on mail volume that averages 900 msgs/day with a 47% spam rate.
Does anyone know what I can check for to eliminate these errors?