SMTP bug

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PeterK2003
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SMTP bug

Post by PeterK2003 » 2009-06-04 12:57

In the SMTP RFC setting "allow empty sender address" check box is logically inverted. When it is checked it should allow empty address however i have have it unchecked and it is giving me a configuration warning b/c i am allowing empty senders.

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Peter

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martin
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Re: SMTP bug

Post by martin » 2009-06-04 18:50

What is the exact warning text you get related to "allowing empty senders"?

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PeterK2003
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Re: SMTP bug

Post by PeterK2003 » 2009-06-04 19:02

W002 - High
You have configured hMailServer not to allow email with empty sender address. Many email server will not accept email from your server with this configuration.
this is with the box unchecked which, to me at least, means that they are not allowed.

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Re: SMTP bug

Post by martin » 2009-06-04 19:10

Is it just me or do you maybe need to read those two sentences in the warning one more time..?

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Re: SMTP bug

Post by PeterK2003 » 2009-06-04 19:23

umm ok dyslexic moment.

But i am still not sure that it makes sense. Why would an SMTP server not accept mail from me if i didn't allow empty sender address? Wouldn't i be rejecting mail that didn't have a sender?

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Re: SMTP bug

Post by martin » 2009-06-04 19:26

> Why would an SMTP server not accept mail from me if i didn't allow empty sender address?

When you deliver a message to another server, and hMailServer tells that server that the email is from someone@yourdomain.com, the recipient server may connect back to your server and issue the commands

MAIL FROM:<>
RCPT TO:<someone@yourdomain.com>

If your server rejects the empty mail from address, the recipients server may reject your message since it was not able to confirm that your sender address was valid.

This make sense. :)

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Re: SMTP bug

Post by mafr1 » 2009-06-04 19:37

Thank you Martin, 'cause I also had trouble understanding it.
Now it make sense. :wink:
Marco
hMailServer 5.3.1-B1748

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Re: SMTP bug

Post by PeterK2003 » 2009-06-04 19:39

ohhh ok. I was very confused as to the intent of the setting.

Is this Part of the RFC? it seems to me that it would be better for them to add a "check sender exists" command. Just seems a bit of a hack to do it this way.

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Re: SMTP bug

Post by martin » 2009-06-04 19:44

The SMTP RFC specifies the protocol. Not so much on how it's supposed to be used exactly.

> it seems to me that it would be better for them to add a "check sender exists" command.

There is. It's called VRFY if I recall it correct. It's disabled on almost all mail servers (including hMailServer) since it just makes it easier for spammers. So no servers actually relies on it and some use this method instead.

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Re: SMTP bug

Post by PeterK2003 » 2009-06-04 20:27

hmmm interesting but couldn't spammers do the same with "MAIL FROM:<>
RCPT TO:<someone@yourdomain.com>"?

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Re: SMTP bug

Post by martin » 2009-06-04 20:36

Sure. But many spammers sends from addresses which doesn't exist anywhere and then this method works.

Please let me know if you find an anti spam mechanism which always works. ;-)

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Re: SMTP bug

Post by PeterK2003 » 2009-06-04 20:40

martin wrote:Please let me know if you find an anti spam mechanism which always works. ;-)
Blocking Port 25?

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Re: SMTP bug

Post by martin » 2009-06-04 20:41

That couldn't be considered as "workable" since it will block some percentage of the legitimate email as well. ;-)

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Re: SMTP bug

Post by PeterK2003 » 2009-06-04 21:11

martin wrote:That couldn't be considered as "workable" since it will block some percentage of the legitimate email as well. ;-)
I know some people that would find that to be a great feature.

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