Alternate SMTP Port

ISPs are clamping down on port 25, preventing users from using 3rd-party SMTP servers such as Birdhouse’s, even with authentication. Some have even gone as far as requiring outbound mail to belong to a domain the ISP knows it controls. All a well-intentioned — but naive — attempt to thwart spammers.

Unfortunately, the trend makes it difficult for Birdhouse to offer SMTP services to a lot of customers. At this point, I simply recommend up front that people use their ISP’s SMTP for outgoing mail.

Now add to this the hassle of using a laptop and traveling from place to place — I hear from some customers who are changing their SMTP servers several times a day. And I hate recommending webmail because I myself hate webmail with a passion.

Solution: Birdhouse needs to open an alternate SMTP port, which people could use from anywhere. cPanel makes this easy to do, but the question is, which port to use for the SMTP alternate? In the first few hours of experimentation, have already discovered that SBC/Yahoo! also blocks port 26, which is the cPanel recommendation. In fact, some ISPs may be preventing their customers from using all non-standard ports.

mneptok helped to clarify the question: Need to choose a port that’s common enough to not be considered non-standard, but that we also don’t need for anything else. If you’re using one of the big commercial providers for connectivity and have found surprising ports blocked, let me know!

I remember in the early-mid-90s, it was still possible to find wide-open public mail relays, and it wasn’t even considered a problem. Now it’s hard even to use closed private relays. Doing business in a world full of bad guys is a drag.

Music: T.Rex :: Chariots of Silk

11 Replies to “Alternate SMTP Port”

  1. Hmmm…common but not used by anything (or anything important ;) How about port 79, used by ‘finger’ ? Finger is questionable from a security perspective anyway, so I wouldn’t suggest running fingerd on most systems.

  2. Matt – Expense is the only obstacle to that one :) Someday we’ll grow to the point where that will be feasible.

    David – Yeah, the security issues around finger probably mean that port 79 is often blocked.

    What I really need is some kind of chart showing port blockage or control by major ISPs.

  3. Great tip Mark, thanks. Investigating now to see whether SBC and others are leaving it open.

    Matt, the other semi-obstacle is that the 2nd server would need to keep an active replica of all legit email addresses and passwords from the master server. Not impossible, I’ve just never set up a scenario like that and would need to investigate how to make it work.

  4. What about port 21? Since you [wisely] don’t allow standard FTP, how about using that port for something else? Or is there a technical reason why that isn’t possible?

  5. jc, I like the way you think, but don’t want to cut myself off completely from enabling FTP for a customer who needs it briefly for some reason.

  6. I hear from some customers who are changing their SMTP servers several times a day.

    If they run Windows, and the Port-587 thing can’t be made to work for some reason, then they might find this useful.

  7. Interesting, Mark. Thanks for posting that.

    On that note, OS X’s “Location” manager is so incredibly useful, and so good at letting you move a machine from work to home and just keep working, all network settings bundled up and switchable on the fly, that it’s surprising that the Location manager doesn’t include SMTP preferences as well. That would really complete the picture.

    Time to hit the OS X feedback button again :)

  8. At this point I’m waiting for next week’s switch to SBC DSL so I can test for myself with alternate SMTP ports work and which don’t. So far 587 looks like a wash.

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