I'm wondering if I have to include the SPF of any ISP used by my customers to send email with an email hosted on my server.

Example : they use Bell to send email for [email protected] (where example.com is hosted on my server).

Basically, because port 25 is disabled by their ISP, they use their SMTP to send emails. This means that Gmail, Hotmail, etc. see an email sent by Bell (example) but the domain is on my server. The result is a softfail because I end my SPF record with ~all.

Sometimes, it's a local Exchange that handles all email deliverability and they can't use my SMTP.

In a long/short term, can this be a problem for my reputation?

My server doesn't accept clear text authentication, neither authentication through port 25. Only SSL/TLS is allowed.

2 Answers 2


As far as I am aware adding the SPF won't work in this instance as I have had problems with it in the past. The way I have been able to solve this is to have clients contact their ISP and provide them with the reason why they need port 25 opened. Many ISP's block it by default to help deal with spam but if your clients contact their ISP and state that they need to connect to their web hosts SMTP server to send emails then the web host should unlock it for them in particular to be able to send emails using your SMTP server and then you shouldn't have any issues from then on.


Such emails are supposed to be sent directly from the user's email client to an SMTP server you control, on port 587 (submission) with user authentication (and STARTTLS). Port 25 is inappropriate for this, for the reasons you've already run into and others.

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