DNS server: PTR record?

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fe31nz

1232 posts

Uber Geek

#1605718 7-Aug-2016 00:56

One other consideration if you want to run your own email server - when your network is down or your email server is down, you need to have a backup MX server somewhere otherwise you will lose emails. The best option for a backup MX server is in some other country that is likely to be unaffected if someone hooks an anchor on the Southern Cross cable and breaks it. Really good backup MX services will have multiple geographically spread servers that will all accept your emails. But a good backup MX service is not so cheap. And having a backup MX service negates some of the advantages of running your own SMTP server, as some spambots send to the MX server without ever trying the main SMTP server address. I currently use DuoCircle:

https://www.duocircle.com/email/email-backup-mx/

which is an excellent service, but you pay for what you get.

jarledb

Webhead
3257 posts

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#1605724 7-Aug-2016 03:06

Any MTA that handels email correctly will queue email when a mail server does not respond. So you shouldn't loose any email.

Mind you, if you run your own DNS on the same network and have no secondary DNS server off the network and your line goes down, the MTAs will see the domain as non excitant and give up right away.

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fe31nz

1232 posts

Uber Geek

#1605725 7-Aug-2016 05:57

jarledb:

Any MTA that handels email correctly will queue email when a mail server does not respond. So you shouldn't loose any email.

It varies from one MTA to another, but these days they will rarely keep trying for more than a day. Outages on a home SMTP server that has sufferred, for example, a hard disk crash, can easily be longer than that. I had my email server down for a week when its motherboard died. And what happens if you are away on holiday and something happens? You might not be back for a week or two.

kiwirock

685 posts

Ultimate Geek

#1644469 3-Oct-2016 03:09

Yeah. The defaults on my mail server were only 4-6 re-tries and 60 minutes between each when I installed one.

I too am a tinkerer and find it easy to flick photo's and the odd zip/mp3 between wireless devices at home by just emailing them. So I have a mail server with no PTR record and Bigpipe as my ISP similar to the O.P.

I use 1stdomains for my registrar, DNS and have a few pop3 accessible hosted mailboxes. I've always found them easy to use. Having a mailbox with them means you can authenticate and relay as well. So that's the PTR sorted, it is sent upstream to someone with a matching PTR. It's not as ideal as direct delivery but it's a small price to pay.

I only have a few important mailboxes for me and family so I use their 5 mailbox email service rather than a secondary MX service with someone else.

If my own server is online I can have as many mailboxes as I'd like. I reserve the few important ones to have on their MX though too.

This is better than a catch-all secondary MX prone to spam. There's no forwarding queue that could eventually fail delivery either unless their 4 MX's are unreachable too. They are kept in pop3 accessible accounts. When my server comes back up should it ever go down, it just remote pop3's in and downloads the email.

This way I don't have to have a separate internal and external email account for when I'm flicking photos and a few tunes between devices at home and don't need to worry about additional apps to access Windows shares from my Android devices etc...

When I get up in the morning, all my email downloads instantly and any email I want to send last minute before jumping out the door it's flicked to my server where it can then take it's time over my old ADSL connection without me having to wait around with the device in question.

I do periodically check for any auto-banned IP's of any spam bots and chuck them in my router's policy routing table as a 'network unreachable' ICMP reply. They give up after a day or odd re-try attempts. However I find this process an interesting thing to track and watch now and then.

edit: I'm moving address soon, and all I need to do is update an A-record or change it to a CNAME (which only has a TTL of 5 minutes) for families devices to start fetching mail from my hosting provider for a few days without them having to re-configure anything. As their clients check every 10 minutes, I can disable external-to-local SMTP for 10 minutes, then update the A-record and wait 5 more minutes before shutting my local server down.

It's all very much overkill, but it offers convenience and keeps what doesn't need to go out on to the net, local.

kiwirock

685 posts

Ultimate Geek

#1644470 3-Oct-2016 03:41

One other small thing... nothing to do with PTR but you may come across this running your own DNS:

When switching a device such as smart phone from 4G to local Wi-Fi and to internal DNS, If you leave it to still hand out the public IP to internal clients, it has to traverse your NAT router to reach the private IP address of the internal server unless you have a public IP assigned on it?

This is the only thing I find annoying switching between external to internal networks to reach my internal server.

As I only have ports forwarded to one internal server, I dodge it up by putting the public IP as a /32 on the server. Then my core router (which comes before my Internet NAT Router) forwards packets for my public IP direct to the server instead.

I could just hand out private IP's to LAN clients, however the old public resolved IP record usually hangs around on the client device long enough to break it for a while until the records all expire and are re-requested.

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