ESA - What happens to email if listeners are suspended?

[esa_fresa]

We're performing an upgrade and will need to reboot our ESA (C100v). We were told to suspend the listeners prior to reboot and make sure there's no mail left in the queue. My question is, does our email server still receive emails while the listeners are suspended?

This is non-clustered. We have just the single ESA device.

[dmccabej]

Hello,

The ESA will not accept any incoming connections while the listeners are suspended. What this typically means is that any mail destined for the ESA will be queued up on the prior-hop MTA until the upgrade has been completed and you resume the listeners. The reason this is recommended is because you do not want the ESA processing anything during an upgrade, because for one the ESA reboots during an upgrade (no mail coming through anyway), and for two you don't want to take the chance of any kind of corruption and/or data loss. 

EDIT: On the chance you're referring to the ESA completing delivery to your internal Exchange/MTA/ETC, then yes the ESA will continue to deliver and flush out its queues while the listeners are suspended. The only time this is stopped is if you also suspend the delivery. 

Thanks!

-Dennis M.

[esa_fresa]

Thanks for the reply Dennis. I think that answers my question. To clarify a little further, the prior-hop MTA would typically be the senders email server, correct? Will users sending mail to our domain receive a "could not be delivered" message? And I assume this means no one in our domain will receive email during the upgrade?

We're sort of trying to figure out if this requires a maintenance window or not.

[dmccabej · Accepted solution]

Correct, the prior-hop MTA would be the sending mail server. The sending server will receive a 'connection refused' message and should continue to hold that piece of mail in its queue, either until it reaches the bounce limit or until it's able to successfully reach out to the ESA and deliver the email. 

Since there's no mail flowing in, you're also correct that no email would be received during the upgrade. 

I would recommend a change window since you never know what can happen. :) Single ESA should complete in roughly 30 minutes without issue, but you'll probably want to give yourself at least an hour or two in case anything goes not as planned. 

Thanks!

-Dennis M.