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I'm sending out automated emails to some users and I get this error message back on undeliverable emails. The strange thing is that it's for only one domain (*@t-online.de).

What multiple parameters does it mean?

(Strangely, I'm also getting bounced by another domain *@gmx.de for multiple users stating "User is unknown {mx063}".)

Is this related to DNS PTR records? The email server I am using has only recently been set up.

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migrated from stackoverflow.com Jul 14 '10 at 1:01

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What implementation of SMTP are you using? –  You Jul 10 '10 at 19:55
Hi, I'm using SmarterMail 6.9 –  alj Jul 11 '10 at 21:51

2 Answers 2

up vote 1 down vote accepted

The RFCs governing the SMTP protocol state that the HELO statement should have only one value.

HELO mailer.example.com
250 mailer.subdomain.example.com Welcome, mailer.example.com, glad to meet you
MAIL FROM: postmaster@example.com

If the HELO statement has a space in it for some reason, some mailers will see that as something extra and puke on it. Others will just ignore it.

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Cheers for that sysadmin1138. –  alj Jul 15 '10 at 7:55

.... just incase anyone else has the same problem, you have to go into Admin and set the HELO property to your domain.

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This answer is of no use unless you tell us what email server you're using –  Mark Henderson Jul 14 '10 at 1:24
... SmartMail 6.9 ... as in the comments above. –  alj Jul 15 '10 at 7:54

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