Hi,

I have recently set up a mail server for multiple domains with postfix and dovecot. Everything is working ok however I have a question about postfix behaviour that hopefully someone can answer.

What happens when there is a network outage and my mail server is not reachable? Will the email fail and be returned to the sender or will it be queued for delivery later?

The reason I'm asking is because I'm wondering whether or not I need to set up a backup mail server.

Thanks,
Paddy

well it really depends on the policy of the mail server that is trying to connect to you. most mail servers will have a set of backoff times, e.g. try every 3 minutes for an hour, every 30 minutes for 12 hours, every 3 hours for a week, then give up. it's up to them though, and it'll only be the very last server to have the email that has a say over it. it depends how critical the emails would be as to wether you'd look towards your own backup mechanisms. there are plenty of services available who will act as a secondary mx for you, i.e. be used by a third party only when your mail server is down. this service would then be within your administrative control and would then spool your mail indefinitely until you resurect your main server, and will then have the spooled mail forwarded on to you. this can also be done by a benevolent friend with their own server too... depends who you know.

Thanks for the info. The emails aren't critical, mostly just personal but I would hate to miss some ha ha! What happens if the backup MX dns record is also being hosted by BIND on the dedicated server. If the server is down will the backup MX never be resolved, or are all the zone records cached to local isp's? Sorry if that doesn't make sense!!!

Paddy

i'd not personally recommend holding your own DNS records for that very reason. if it's a home affair, try a site like zoneedit.com which will hold your dns for free.

The server is in a datacentre so it's pretty reliable but it does get brief spurts of downtime. Zoneedit are great I'm currently using them, pity only the first 5 domains are free!

well if you can remember another username and password....

actually though, do the data centre not host resilient dns offsite anway? sems pretty reasonable to me.

Very true ha ha! Yeah they do ofer DNS hosting for free with the package but they don't have a user interface so I have to submit a support ticket everytime I want to make a change which is a pain! Think I'll stick with zoneedit.com for the moment.