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I am having an intermittent issue with sending mail via my asp.net mvc application. It doesn't always happen, but it is happening a lot.

Here are some of the errors:

Message delivery to the host '68.87.26.147' failed while delivering to the remote domain 'comcast.net' for the following reason: An SMTP protocol error occurred.

Message delivery to the host '207.115.11.16' failed while delivering to the remote domain 'bellsouth.net' for the following reason: An SMTP protocol error occurred.

Message delivery to the host '98.138.112.38' failed while delivering to the remote domain 'ymail.com' for the following reason: An SMTP protocol error occurred.
 The SMTP verb which caused the error is 'MAIL'.  The response from the remote server is '421 4.7.1 [TS03] All messages from xxx.xxx.xxx.xxx will be permanently deferred; Retrying will NOT s'.

Message delivery to the host '64.98.36.4' failed while delivering to the remote domain 'trigasco.com' for the following reason: An SMTP protocol error occurred.
 The SMTP verb which caused the error is 'HELO'.  The response from the remote server is '504 5.5.2 <WIN-OB929P97YAR>: Helo command rejected: need fully-qualified hostname
'.

Message delivery to the host '66.196.118.36' failed while delivering to the remote domain 'yahoo.com' for the following reason: An SMTP protocol error occurred.
 The SMTP verb which caused the error is 'MAIL'.  The response from the remote server is '421 4.7.1 [TS03] All messages from xxx.xxx.xxx.xxx will be permanently deferred; Retrying will NOT s'.

My settings for my smtp virtual server are as such:

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I have added 127.0.0.1 to the allowed list. I am getting some emails out, probably half of the ones that are attempted.

I am using a dedicated server with a public ip address. It is not part of a domain.

Any suggestions?

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There are a few things going on here. Let's break them down:

4.7.1 [TS03] All messages from xxx.xxx.xxx.xxx will be permanently deferred;

Notice that this happens for Yahoo! and ymail - you're on their shitlist. Maybe you spammed someone there; maybe someone who owned this IP prior to you spammed them, maybe your reverse DNS indicates it's an IP address on a PPPOE connection and they block them because of the high rate of spam. Not your mail server's fault though; so nothing to see here.

 The SMTP verb which caused the error is 'HELO'.  The response from the remote server is '504 5.5.2 <WIN-OB929P97YAR>: Helo command rejected: need fully-qualified hostname

This one is reasonably self explanatory - your mailserver is not configured with an FQDN. This mail server requires you to state who you are when you mail them; probably so that they can run a reverse-DNS or something to match what you say with what you send.

Message delivery to the host '207.115.11.16' failed while delivering to the remote domain 'bellsouth.net' for the following reason: An SMTP protocol error occurred.
Message delivery to the host '68.87.26.147' failed while delivering to the remote domain 'comcast.net' for the following reason: An SMTP protocol error occurred.

These are the real ones you should be focussing on. I would break out your wireshark/pcap, capture your mail traffic and then step through it to see what's going on. Re-create via telnet if you must. This will give you a better idea of what errors are going on. Maybe they're your problem, maybe they're not.

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  • Yeah, I'll prob use an external smtp. Like you said, someone with this ip previously probably got it banned. Seems like more of a hassle than it's worth to get them unbanned. Thanks!
    – JohnDoe
    Jan 8, 2014 at 5:13
  • Probably a wise move, unless you're sure that your IP space is "clean"
    – Mark Henderson
    Jan 8, 2014 at 21:12

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