What must one do to avoid Gmail's retarded non-spam filtering?

[Erik L <erik_list () caneris com>]

I realize that this is somewhat OT, but I'm sure that others on the list encounter the same issues and that at least 
some folks might have useful comments. 

An increasingly large number of our customers are using Gmail or Google Apps and almost all of our OSS/BSS mail is 
getting spam filtered by Google. Among others, these e-mails include invoices, order confirmations, payment 
notifications, customer portal logins, and tickets. Almost anything we send to customers on Google ends up in their 
spam folder. This results in a lot of calls and makes much of our automation pointless, never mind all the lost sales.

The problem is compounded by those who use mail clients and do not log in to the webmail at all, since they would never 
see the contents of the Google spam folder.

We have proper A+PTR records on the edge MTAs, proper SPF records for the originating domain, proper Return-Path and 
other headers, and so on. There isn't anything that I can think of other than the content itself which would be 
abnormal, and obviously the content is repetitive and can't be changed much. Is there something obvious which we've 
missed?

Aside from the following clearly impractical solutions, what can we do? 
1. Asking everyone (including those we don't even know yet) to whitelist all of our addresses, to check their spam 
folders, and to click on "this is not spam"
2. Providing our own free e-mail service to everyone (including those we don't even know yet) and putting up "don't use 
Google" ads on all of our customer-facing systems

At least this isn't Hotmail where mail is just silently deleted with no NDR after it's accepted by their MTAs.

The call volume has been going up instead of down lately and it's gotten to the point where we're sending MTA log 
extracts to people to prove to them that we really did e-mail them. 

Would greatly appreciate any advice.

Erik