For a variety of reasons, Mercury is quite strict about enforcing the syntax of the MAIL FROM: and RCTP TO: SMTP commands. The main reason is that syntax errors in these commands are a common indicator of spam (no properly-written SMTP client should ever be getting the protocol this badly wrong). The secondary reason is that a number of open relay testers use deviant or invalid forms like this as part of their test, and evaluate the server based on how it handles them.

As Thomas has pointed out, the syntax for these commands in RFC2821 is quite specific - you can't just throw any address format in there. If your mail clients are getting this so badly wrong, you need to get back to their authors and suggest that they re-read RFC2821, then correct their code.

Cheers!

-- David --

I tried several applications with Mercury, such as wordpress and limesurvey. But I got mailing errors. The error is weird. Mercury can not recognize "Mail From". If "Mail From" is like "FirstName LastName <name@mydomain.com>", mercury will report 501 syntax error or say it is invalid address. But if "Mail From" is like "<name@mydomain.com>", mercury could deliver.

 I am so confused and do not know why. I am now using Mercury on my testing server and relay to our mailing system via Mercury smtpE end to end client module. But why this problem happened? I will reapply appreciate for any inputs on that. I am stretching my hairs.
 

IAW RFC 2821 the syntax of the MAIL FROM: command is

      MAIL FROM:<reverse-path> [SP <mail-parameters> ] <CRLF>

Where the reverse path is the SMTP email address of the sender.  Note that the personal name that yuo are using is not allowed.  These applications should allow 

you to enter a simple SMTP email address either with our without the <> as required.