When in doubt, I often just telnet into the SMTP server (port 25) and try the commands manually:

HELO domain.com
MAIL FROM: user@domain.com
RCPT TO: user@destination.com
DATA
..<blah blah>

Some SMTP servers are very lenient and some are very strict. Try your best to stick to the RFC and I think you'll be safe in any case:

http://www.ietf.org/rfc/rfc0821.txt

In reply to Re: Re: Re: Net::SMTP generates unexpected errors in Debug Mode by ChunkyMonk
in thread Net::SMTP generates unexpected errors in Debug Mode by gary kuipers

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