Slovakia-based communications provider Slovak Telekom, a 100% owned subsidiary of Deutsche Telekom, has terminated all email services effective December 31, 2020.
Mailkit's Jakub Olexa explains: "The affected domains are @stonline.sk, @mail.t-com.sk, @t-zones.sk, @posta.telekom.sk and regional subdomains of telekom.sk eg. (bb.telekom.sk, ke.telekom.sk, ba.telekom.sk, etc). It also affects a number of business domains that were hosted at their email service and have not made the switch to their business service. All affected domains can be identified by using MX of mta-in.telekom.sk. It's likely that the business customers will switch to a different service (or at least some of them) but the above listed domains should be the ones with the bulk of the volume and should be put on suppression lists as abandoned domains."
Thank you, Jakub, for sharing this very useful information!