Frequently Asked Questions


Non-customers can find answers to their questions here regarding e-mail delivery to Belgacom customers, as well as Belgacom customers that may have questions regarding our relaying services.

  • Senders' FAQ
    This section answers questions for people that are sending e-mail to Belgacom customers from outside the Belgacom network.
  • Users' FAQ
    This section answers questions that customers may have regarding sending mail from and to their Belgacom e-mail account.
  • Port 25 FAQ
    This section answers questions and concerns regarding the blocking of port 25 for dynamic IP DSL customers.



Senders' FAQ


Q: Does Belgacom operate a "whitelist" or "allow list" that I can get added to?
A: No. An allow list is a "free pass" which allows e-mails from specific senders to bypass any type of mail filters and other precautions.

Q: What's the maximum allowed message size?
A: The largest piece of e-mail that Belgacom will accept from or to the Internet, is 16MB. This includes all mail headers, body text, and potential attachments combined. This is a fixed maximum, and cannot be changed.

Q: Why is my SMTP connection being closed with a 5xx permanent error?
A: Below you can find the possible permanent error codes, and things you can do to prevent them.

  • 5xx Under investigation for spam abuse

Q: Why is my SMTP connection being closed with a 4xx temporary error?
A: Below you can find the possible temporary error codes, and things you can do to prevent them.

  • 421 Too many connections from your host

  • 457 Too many invalid recipients

  • 458 Too many recipients (RL)

  • 459 Too many recipients (RL)



Users' FAQ


Q: How many connections am I allowed to open to the Belgacom ISP relay service?
A: The maximum allowed simultaneous connections is 3 per broadband IP address.

Q: Are there any restrictions on the number of e-mails I can send from my PC?
A: Yes, there are. Unauthenticated clients are allowed to send maximum 720 mails per hour. If you are in need of going above that generic limit, you must use client authentication through the mail submission port.

Q: How can I send messages over a secured channel?
Your client should be configured as follows:
   relay server: relay.skynet.be (port 587, TLS required)
   user name: yourlogin@skynet.be

Q: Can I use the Belgacom ISP relaying service from outside the Belgacom network (roaming)?
A: Yes, by using SMTP client authentication with TLS (encryption) enabled. See above for more details.

Port 25 FAQ


Q: Why can't I connect to any SMTP service outside of the Belgacom network?
A: Most likely, you have been assigned an IP address from our dynamic IP pool. That means that you are having a consumer DSL product, that is not allowed to connect to any other mail relaying service than the Belgacom ISP relay (relay.skynet.be). Access to any other SMTP service outside of the Belgacom network, has been deliberately restricted, to protect our customers.
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