Customer has performed an upgrade on Symantec Messaging Gateway from version 9.5.4 to 10.0.x and is unable to receive email messages from some external senders. However, customer is able to receive email messages from the same senders when they use SMG 9.5.4.
After EHLO command, the following error appears in the packet capture.
421 4.4.2 service timed out.
Extra space in 'size' attribute inside EHLO response causing failure with qmail.
'250-SIZE ########' has two spaces between 'SIZE' and the number value.
Upgrade to SMG v10.0.2 which addressed the issue.