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Plusnet SMTP Server IP Addresses

shamus
Grafter
Posts: 114
Registered: ‎13-08-2007

Plusnet SMTP Server IP Addresses

I run my own SMTP server and want to restrict inbound connections to this server to my AntiSpam provider and plusnet servers only.

My AntiSpam provider has a list of IP's, but I can find no such list for Plusnets SMTP servers. Does anyone have a link or list of the current Plusnet SMTP servers that would route email inbound to my server?

 

3 REPLIES
MrSilver
Pro
Posts: 550
Thanks: 88
Fixes: 9
Registered: ‎05-10-2016

Re: Plusnet SMTP Server IP Addresses

Couple of tests you could try

tun tcpdump / iptables log mode or similar on SMTP port and check what IPs are delivering mail, sane mail to yourself to check what IPs are coming in from.

Plusnet smtp servers are advertised as stmp.plusnet which resolves to 2 IPs

smtp.plus.net. 86399 IN CNAME relay.plus.net.
relay.plus.net. 86399 IN A 212.159.9.107
relay.plus.net. 86399 IN A 212.159.8.107

So would go with those 2 to start with in the absence of any official statement.

Plusnet may well change SMTP server IPs too at some point, so you may want some simple script that is checking the DNS resolves to the same IP still, something like

dig smtp.plus.net results into a file

diff the file with the known output

when diff is not null flag error

run in a crop job once a day

shamus
Grafter
Posts: 114
Registered: ‎13-08-2007

Re: Plusnet SMTP Server IP Addresses

Looking at my logs I can see previous connections of inbound mail from Plusnet from the following server:

avasout01.plus.net (84.93.230.227)

So I am not convinced that smtp.plus.net or relay.plus.net are anything to do with inbound mail. Maybe these are just used for outbound...?

Would be nice if there was a definitive list... I don't want to restrict the server and then find I miss email as the connection has been refused as the email comes from a different host.

 

Superuser
Superuser
Posts: 9,813
Thanks: 1,189
Fixes: 68
Registered: ‎06-04-2007

Re: Plusnet SMTP Server IP Addresses

The Plusnet relay IPs are listed in the SPF txt record for madasafish.com. These will have host names like avasoutxx.plus.net where xx are numbers. If you are doing your own email collection it will be these relays that pass the message onto you.

relay.plus.net will be a load balancer upstream of those IPs.

David