Airport and Verizon DSL SMTP issues

I have Verizon DSL with a westel DSL Modem connected to an Airport Base Station (dual), which has one desktop 450 G4 connected via an ethernet Intel Hub, and another older G3 PB using an Orinoco Gold wireless card. I am having a problem sending attachments larger than 90K when connected through the ABS. (I've tried several mail programs, including the mail.app and Entourage in OS X and Outlook Express and Netscape in OS 9.2.2) I don't have the problem with the G4 directly connected to the DSL modem. Verizon tells me that they have upgraded their SMTP servers, and the work around is to lower the ABS MTU rate to 1452. Apple says the MTU rate is firmware controlled, and is not really responsible for what Verizon does with their server software. They also seem surprised because they claim that the MTU rate is managed the same way by both the G4 and the ABS, when directly connected to the DSL modem. Has anyone else run into this issue and/or can anyone offer any suggestions?