Internet access from work

Hello,

to check my e-mails during lunch break I'd much prefer to use portable Thunderbird than clunky Webmail. Portable Thunderbird works fine from home, but at work, it is denied access. To go on the internet at work, I need to supply a work user ID and password that are different from that for my personal e-mail account. The problem is it's not clear within Thunderbird's interface where that extra ID and password should be entered.

Does anyone have experience of storing 2 separate IDs in Thunderbird, so it has one to get on the internet in the first place and a second to get through to a Webmail account?