I have been running ISPconfig for a good 6 months on one server and found that someone was trying to send me a message abour 10MB of size. Turns out that I cant accept that size of message? Where can I go and change that. The ISPconfig system shows that I have unlimited space (-1) but thats not the same as maximum message size per message. I searched the forums, cant find this question asked, I assume it should have been asked.
I wouldn't raise that limit. Most mailserver limit it to 10MB so if you start sending mails bigger than 10MB they will most likely be refused by the other ones.