Re: ISP port blocking practice

With all the different webmail systems, it seems unlikely to me (though I definitely wouldn't say impossible) that bots are spamming through your webmail (unless you work for gmail, hotmail, etc. and are an attractive enough target that it made sense to code a bot to automate utilizing your webmail interface).  Bots being used as proxies seems far more likely to me for the general case of "bots" spamming through an ISP's webmail.

Many providers and hosts use the same webmail packages so the work to automate is a bit lower than one might think. We have seen bots sending spam using our squirrelmail and roundcube webmail using credentials gleaned from phishing activity.