Lost Mail when DNS host unable to resolve

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Posts: 5
Joined: Tue Jul 11, 2017 9:50 am

Lost Mail when DNS host unable to resolve

Post by stetters »

Hello all,

We have a client that uses MailEnable standard to Smarthost mail from automated processes onto O365 for delivery to internal users / clients.
The SMTP server within MailEnable is defined to SmartHost all mail to O365. As all the mail received by the smarthost is generated by automated systems, we have disabled the option of NDR generation.
This setup works well and has done so for many years.

However, recently, the client has been transitioning DNS servers and as such, the MailEnable service was interrupted for a period of time while the new DNS servers were updated.
During this time, the server on which MailEnable runs, lost the ability to resolve DNS.

To our surprise, this resulted in a loss of some emails processed through MailEnable as even though the SMTP delivery options are set to retry every 5 mins, with a failed message lifetime of 100 hours, due to MailEnable not being able to resolve the O365 host via DNS, the message was immediately failed with a "DNS Lookup failure (11001) error, followed by a return to sender message, and, as we do not enable NDR reports, the final message was "NDRs disabled. Deleting failed outbound message"

We have never experienced this situation before and I would expect that there will be circumstances at some point where DNS requests may fail / timeout again so wish to circumvent the loss of any mail moving forward.

Reading previous posts, I can see that the DNS failure alerts do not perform any retry function by design. Given mails have physically been lost as they were accepted by the MailEnable server but deleted before being smarthosted onto O365, I am looking at suggestions on either enabling NDRs but ideally to send them to a specific address or to redirect the MAI files processed by MailEnable via a pickup event so we have a copy of any MAI files should we encounter this issue again.

Thanks in advance

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Joined: Thu Jun 27, 2002 9:35 am
Location: São Paulo, Brazil

Re: Lost Mail when DNS host unable to resolve

Post by lyceepasteur »

I am facing the same problem.
I configured smarthosting with a Microsoft 365 server.
For some reason (slow Internet maybe), the smarthost name could not be resolved.
In that case, messages are deleted from the outbound queue as no retries are scheduled.
- How to configure NDR in case smartHost DNS is not resolving ?
- Is there a way to configure a direct send in case smarthosting is not working ?
Thanks in advance.

Posts: 5
Joined: Tue Jul 11, 2017 9:50 am

Re: Lost Mail when DNS host unable to resolve

Post by stetters »

I have now resolved the issue by adding a pickup event within the MTA which calls a powershell script that takes a copy of the message (header and message files) and locates then into another area. As the header and messages are named the same but held in different directories within the SMTP queue, I followed the same structure in my Save Area

Program to execute on mail file: powershell -ExecutionPolicy Unrestricted -File "C:\MailScripts\MailEnable-SavedMessages\Copy-MailEnable-Messages.ps1"

Create directories to store the saved mail
C:\SavedMail <-- Place header files here
C:\SavedMail\Messages <-- Place Message files here

I also run a scheduled task on the server that maintains this area so that only 7 days worth of mail is retained.

Should the issue arise again, we can simply reprocess the mail items from the saved area

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