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Sendmail Error 550 "email ID assumed to be invalid -Impossible to verify"

Posted on 2003-10-28
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Last Modified: 2010-03-18
I am using sendmail, it works fine for all other domain but recently I got this error, is this a problem with the reverse lookup ? The strange thing is I donot get this error often from otherdomain.com and seems to work fine.

Can you help ?

Error :
  ----- The following addresses had permanent fatal errors -----
<xyz@otherdomain.com>
    (reason: 550 Address "abc@mydomain.com" assumed to be invalid -
Impossible to verify)
<pqr@otherdomain.com>
    (reason: 550 Address "abc@mydomain.com" assumed to be invalid -
Impossible to verify)

   ----- Transcript of session follows -----
... while talking to mail.otherdomain.com.:
>>> MAIL From:<abc@mydomain.com> SIZE=5219
<<< 550 Address "abc@mydomain.com" assumed to be invalid - Impossible
to verify
554 5.0.0 Service unavailable

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Question by:AshishGadkari
9 Comments
 
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Expert Comment

by:paullamhkg
ID: 9640059
After read the error, it's seem the party otherdomain.com refused to receive mail from abc@mydomain.com.

I think otherdomain.com setup the Anti-Spam and reject the mail from abc@mydomain.com.

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by:paullamhkg
ID: 9640068
Have a look here for the Anti-Spam about the sendmail http://www.sendmail.org/~ca/email/doc8.12/cf/m4/anti_spam.html
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Author Comment

by:AshishGadkari
ID: 9640096
Thanks for the quick reply.

I too though so, but then why is it so that the mail gets bounce sometime only, not always?

Is so that I donot have the reverse lookup set for my mail server, if so how can I check that. Although I have checked the reverse lookup of my mailserver from whois and it resolves to IP. but I am not sure is this the correct way to do it.

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Expert Comment

by:paullamhkg
ID: 9640136
I'm also facing similar situation here, still looking for solution(s), and I did serveral testing for the Anti-Spam, sometime the mail still pass through to the mail server, sometime it doesn't, I think there is setting of the Anti-Spam got to be clearly set. may be this is the same case of your otherdomain.com, they setup the Anti-Spam, but so how not set it up clear like me :(
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Expert Comment

by:_tack
ID: 9640474
A lot of sites, now refuse to accept emails from domains that cannot be verified (unresolveable domains)
an easy verification is done by checking the existence of domain using DNS,
if for some reason DNS are not reacheable due to network overload or DNS
software problem, then the MTA assumes that the domain does not exists --> refuse to
accept email.

A better error value for the server on "otherdomain.com" should be 450,
but then a lot of mail servers might try to deliver spam mail for days, this will just cause
unwanted network traffic.
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Expert Comment

by:owensleftfoot
ID: 9640699
Is your domain a valid domain with dns records or is it just what you have called your box? If its not a valid domain you can get around this by using your isps mailserver in the "smarthost" setting of your sendmail.cf. Some mailservers will reject mail if the domain it is coming from is "invalid".  
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Expert Comment

by:brabard
ID: 9662583
I think the situation is one and the same everywhere . Sysadmins are growing up using of reverse lookup all the time .
I was in the same trap , and fix it after building a master dns server .
But , if in your dns zone (managed by your ISP) your server is written proper , you should not have problems .
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