Neil Turner's Blog

Blogging about technology and randomness since 2002

SMTP Servers

I’m having a disagreement with someone over SMTP servers. I’m of the opinion that you should generally use the SMTP server that corresponds with your domain – so my mail should be sent through, and my Gmail messages should be sent through This is because of technologies like SPF and DomainKeys which are, as I understand, dependent on email being sent through the correct SMTP server for that address. For example, if I send a message using my Gmail account through Thunderbird using Gmail’s SMTP server, the message will have the DomainKeys header added; if I didn’t, it wouldn’t and would look more like a spam message as a result since you’d expect Gmail messages to come via Gmail.
It’s also more convinient if you use different internet connections frequently, since you don’t have to change the server every time you use a different ISP – this is especially helpful for laptop users like me who use Wifi hotspots often.
But I’ve been told that this is wrong and that you should always use your ISP’s SMTP server instead. To me this doesn’t make sense – say an AOL user was sending a message, you’d expect it to have come via AOL’s mail server and not some random server.
So who’s right? Should I be using my ISP’s mail server, or the mail server associated with each account?


  1. I’ve always gone along with the same theory as you, if I’m sending an email through my account, i’ll use, etc. I’d only use my ISP’s when the place I have a POP3 service from doesn’t have its own SMTP, or its not working. I couldn’t say which is the “best option”, but I’ve been doing this all the time.

  2. I agree with you. That was even the main reason why I bought my own domain — so when I’d travel, using lots of different IPS’s, I wouldn’t face unexpected problems.

  3. My Uni account and my gmail account go through their respective SMTP server. All the other accounts I have go out through my ISPs mail server, even if they are hosted there or not.

  4. One point for the ‘through your ISP’ argument is that if all users were forced to use their ISP’s SMTP server there’d be a trail of logs leading right back to somebody who signed up for that account.
    If I remember correctly, ISPs (in the UK & USA at least) have to keep server logs by law for x years – if all email can be traced back to an ISP & from there to an account holder the police can find the culprit with relative ease.
    On the other hand, drive-by spamming on open wifi networks and viruses designed to act as mail servers would probably both explode in number (although haven’t they already?)
    Some UK ISPs (I hit this with Freeserve once) are remapping outbound port 25 on domestic lines to their own servers, so you are forced – unless you have a tunnel or server on non-specific port – to use their mail servers.
    BTW I’m being boring and sitting on the fence for now. Both def. have their merits. 🙂

  5. Personally, I use mail.{my domain name} when sending out email from {my domain} and when sending out from my {nodename} email address.
    One the “send out from your ISP” front there is the pros of:
    * Faster connection times
    (As your ISP doesn’t need to “authenticate” you further than the IP address)
    and the Cons of:
    * Easy for viruses to “guess” your ISPs SMTP server
    But on the “use webhosting SMTP” server front there is the pro of:
    * SPF/DomainKeys authentication
    (if supported: most web hosting control panel providers are slow to offer SPF creation facilities)
    Cons of:
    * Some ISPs block external port 25 access
    (some control panel suites offers port “26” access instead to bypass this)

  6. The last I tried, I had to send email through my ISP’s SMTP server because they block anything else. That seems to be becoming practice at many locations. Personally, I would prefer to send through my domain’s SMTP server. I think the reason for blocking is to prevent open relays and spyware turned spam servers.

  7. I use my domain’s SMTP server. It just makes sense to me to send e-mail using that for the same reasons Neil mentions.
    I have yet to run into an ISP that requires me to use their mail server…luckly.

  8. As others have mentioned, there are no absolutely compelling reasons to use an ISP’s SMTP server. I personally use’s mail servers when sending stuff from a address.

  9. I don’t have much choice.
    I could use the SMTP server that sits on my cable modem – but as the IP is dynamic the mails are often blocked by people.
    Instead it is safest to use my ISPs SMTP server as at least the emails currently get through.
    To complicate things further, my domain does not have an smtp service as that is an additional cost for little benefit at the moment.

  10. I use my isp’s mail servers. If I could be bothered to implement SPF on my domains then I would simply add my ISP’s smtp server to the list of trusted mail servers.
    Using your domain’s server takes more hassle to setup and is slower. Plus I pay for bandwidth usage on my domain, whereas I don’t at my isp – so it makes sense to use the cheaper option.
    Also, I don’t want my domain authentication information stored on every computer I use – and it’s a pain to get authentication working with your own local smtp server sometimes anyway.
    Having said all that, I don’t travel with my computers and I tend to use webmail anyway. So I picked the best option for me – which way you do it is up to you.

  11. I don’t think it really matters. The only important thing is to ensure you don’t send direct from your own pc as that will get blocked as coming from a block of dialup accounts. When in england I sent everything through my isp as it was quicker and most people dont have spf set up so it doesn’t matter.
    In the states I tried to use my domain mail server when using popcorn, but for some reason the mail server doesnt like popcorns authentication for some reasonn so i’ve no choice but to use the isp (which is so much faster than the domain server). To send a mail with thunderbird via my domain takes about 1-2 seconds and the interface is noticable as it sends. To send a mail via my isp with popcorn – you don’t even see the send dialog box appear before its closed.

  12. I am obviously a novice compared to you guys, but I am in the UK an find that any smtp outbound mail server I use (Waitose and Virgin) will automatically reject a message if you are not using them as an ISP. My broadband is with Virgin, so if I try to send a Waitrose email using the Waitrose smtp server > automatic reject.