Webmail Problem?

[fulltilt]

I had some trouble with Webmailer in 2.4.7.1 and i installed the omega Webmailer a few weeks ago. It works very good but one of my customer is not able to login:
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He told me that the problem is in both browser IE & FF ...
I'm not shure about this .. and i was able to login from my computer.
Are there known problems - login into webmailer?

regards