Yesterday, TMNet announced that outbound SMTP connections on port 25 will be blocked for Streamyx dynamic IP connections, citing spam control as the reason. No prior notice was given other than an announcement on their website on the day that it's scheduled to be implemented. Yet, we know that they have prepared the migration guide as early as Nov 25 and Nov 27. Have they not the foresight to consider the logistics involved in getting the word out and ensuring a smooth migration?
If you are an end-user facing problems with your (non-webmail) mail provider, you now know who the culprit is. Your provider/IT support should be able to assist you in reconfiguring your email settings to work around the block.
As for email administrators, note that port 587, the RFC standard for mail submission is left unblocked and can be used by your clients. Go the extra mile and set up policies allowing only authenticated mails to be sent through this port. If however you choose to have your clients use the TMNet SMTP proxy, beware of its consequences.
Jeff Ooi has highlighted breach of privacy as one. Besides that, the mails may violate SPF conditions as it originates from TMNet's servers instead of yours. You are also at the mercy of TMNet's operations crew, without control over the delivery queue or any other parameters. They still can't get their DNS server right, can we expect the same from their SMTP relay?
That said, it can't be denied that this block will stop compromised computers from being abused to spam. In a few weeks, we'll be able to assess through senderbase.org the volume of mails reduced from this exercise.
