rusticdog wrote:... snip ...
MailWasher uses the PC usernames for seperate IDs, so the only way to do this would be to have separate user accounts. The only other solution is just not have MailWasher launch the email client after processing and do this manually. However as you can only have one default email client, things like mailto: links and Quick Reply will only ever go through the Windows default mail program. (my highlight)
I'm not entirely certain about this - in short 'it depends'.
Different flavours of Windoze generally store a default email client in the registry which is why it's called if you click on an email address on a web page, for example. I use WIN 7 and have noticed that sometimes I'm asked which email client I would like to use - and it lists a few, including GMAIL (oddly). It happens regularly and unfortunately I can't recall the sequence that triggered this behaviour. I suspect it was something written into the code of web pages / some help systems.
From a programming perspective it should not be difficult to link account A with Outlook, account B with Thunderbird and so on, including calls to open your browser on a web based email service like GMAIL. (Some web based email services have deliberately chosen to make life difficult so you can't access them via Outlook etc - or MWP). Not difficult is not the same as a good thing or something requiring elevation on a developers' "things to do before I die" list.
I'm told that with a bit of fiddling you can probably do what you want (so far as I understand it) with Thunderbird - I've tried and sorta got it to work. My needs might differ from yours though - I wanted to hide my real IP from scammers. I gave up because whichever email client you use locally sends your IP in the email header (unless you go darkside and use nasty naughty tools). Outlook (I use 2007) sorta works for me and apparently you can have multiple accounts stored in their own PST files - I've done it with my RL email address and fake GMAIL ones.
If it's not too intrusive, why do you need this function - as in, what is it that you are trying to achieve? Aside from the advice RD gave you there might be alternate / easier ways for you to do what you want without altering MWP. And if it's something really useful that the developers had not yet considered, your info might make them look a bit closer at the issue.
Cheers,
mike