On 2022-10-20 08:48, Florian Effenberger via mailop wrote:
Hello,
I actually ran into a similar problem last year after a mail server
migration. Here's what I documented back then in my blog:
"Deutsche Telekom, respectively T-Online, by default blocks IP
addresses that haven’t been used for sending e-mails to their servers
for a certain amount of time. You can test if you are blocked by
connecting to their mail server on port 25 – if the blocking is
active, the connection will get immediately dropped with an 5xx error
message, that lists a contact address to request unblocking from. To
test, run the following command from your mail server:
[...]
I wasn't aware of the timing aspect, so thank you for this!
I will prepare a cron job to send an e-mail to my @t-online.de address
(which is pretty much dormant) very week or so, in case this prevents my
servers from dropping off the whitelist..
Cheers,
Bernardo
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