From MTU LUG wiki
Residential accounts are known to have the following ports blocked:
- 21 (FTP)
- 23 (TELNET)
- 25 (SMTP)
- 80 (HTTP)
- 110 (POP3)
Some sources say that if an email server is detected on a residential account, the internet connection will be stopped entirely.
These limitations do not apply to Charter Business accounts.
AT&T (formerly SBC (formerly Ameritech)) also provides DSL service in the area. SBC also blocks outgoing port 25 (SMTP), but does not block other services.