@automatican
Seems pretty freaky to me. There are some additional ports, which might be usable for outgoing connections on most networks like 25, 80, 110, 143, 465, 587, 993, 995.
Anyway, to have the site2site VPN on 443 maks no sense at all. You ISP should not block any outgoing port. Some may block specific P2P ports though.