Exchange 2007: Remote host said: 503 Bad sequence of commands error

As of 11PM last night every every inbound messages get error 503 message to them.  what can I do resolve this issue?  SBS 2008
tips54Asked:
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Manpreet SIngh KhatraConnect With a Mentor Solutions Architect, Project LeadCommented:
Possible issue with Firewall ...... Check for any updates ?
Was there any changes like Admin password changed or something ..... seems Firewall only as Internal is fine and only connection point between Internal\External is your firewall.

- Rancy
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Manpreet SIngh KhatraSolutions Architect, Project LeadCommented:
Can the user send email to themselves ?
Do you receive emails from external ?
Having issues with sending emails to external ? Is there a firewall in between if so any changes made to it can it receive emails from your server and route ahead ?
Is the Transport service running on the Exchange Server ?

Is the NDR getting generated by your server or some recipient server ... if recipient server it seems an issue at their end.

- Rancy
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Manpreet SIngh KhatraSolutions Architect, Project LeadCommented:
Hope DNS resolution is working fine on the server and also check with Send connectors :)

- Rancy
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tips54Author Commented:
Rancy,

The problem seems to be with sending out.  I can send out, I can send to my self or internal just fine.  Every now and then the email from External will get through most of the time you get the 503 error. I do have a firewall (Watchguard) in between and I actually see the error on the firewall as well.  I think the problem is on the firewall but not has been changed.  I also never get the error when I send from Gmail.

Mxtoolbox has been texting me all day saying SMTP IS UP / SMTP IS DOWN
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Exchange_GeekCommented:
503 - Bad sequence of commands.
or
This mail server requires authentication
(also called SMTP Error 5.0.3)
SMTP Error 503 : In the original standards SMTP Status 503 indicates that the commands have been sent in the wrong order, for example your mail server has sent the
"Hello" command before sending the "Mail" command. This can often be caused by a drop in network connection just as your server was sending a command, resulting in
the ISP's server not receiving it and consequently not understanding the command that followed it. Note : this error, particularly if repeated, can be indicative
of communications problems, such as a noisy line, intermittent drops in network connections, etc...
------------------------------
SMTP Reply Code 503 is nowadays more often an indicator that the SMTP server you are trying to use requires authentication and you tried to send a message without authentication (username + password). This SMTP Error 503 is permanent in that the SMTP server, will not log any errors in its log and it will not retry - you will have to resend the email using authentication. Example of such an error : "SMTP Error (state 13): 503 This mail server requires authentication when attempting to send to a non-local e-mail address. Please check your mail client settings or contact your administrator to verify that the domain or address is defined for this server."

Ref: http://www.aspiresoft.com/email-server-status-codes/

Regards,
Exchange_Geek
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Exchange_GeekConnect With a Mentor Commented:
Couple of points that quickly come to my mind.

=> Reboot the firewall, patch and update it, contact their support and get the help you need.
=> Paste the firewall logs - that's if you feel sake for us here to review it.
=> lastly, check if the firewall foes into hung state wherein connections *might* get dropped.
=> Also, check if the drive Exchange holds its SMTP logs isn't going too less in size, as in below 500 megs or something.

Above points might be repeated of the above poster, however just want it to sequence it for you.

Regards,
Exchange_Geek
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Manpreet SIngh KhatraSolutions Architect, Project LeadCommented:
Were you able to figure out the firewall issue and fix it ?
If not try to over-ride and work directly with email TO and FROM the exchange to avoid any email losses.
Let me know if you need any assistance.

- Rancy
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tips54Author Commented:
I was able to get this resolved by Enabling ESMTP on the smtp proxy.
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Manpreet SIngh KhatraSolutions Architect, Project LeadCommented:
Ideally it should have been as it was relaying emails ....... was any other changes made apart from that ..... but pretty wired how that went away if it was working good earlier :(

Anyways issue resolved so alls good :)

- Rancy
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Manpreet SIngh KhatraSolutions Architect, Project LeadCommented:
Its good we tried our best to fix the issue.
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tips54Author Commented:
good point Rancy. I don't understand either how it was working fine before without changing ESMTP.
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Manpreet SIngh KhatraSolutions Architect, Project LeadCommented:
Is the issue resolved :)
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Exchange_GeekCommented:
Firewall, firewall, firewall - all i read in mine and Rancy's post was to check the firewall - and you did it.

You've gone ahead and solved it my friend.

Regards,
Exchange_Geek
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tips54Author Commented:
thank you.
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