Not delivered e-mails!

Hi!
I have a problem with my TB. I have installed it on my Pen Drive (Kingston Data Traveler II - 512MB). The problem is, that many of e-mails sent using TB have been never received by recipients - there is no rules. I am sure that everything is OK, all POP3, SMTP data are correct... I have imported settings from my Outlook Express.
- all e-mails sent from Outlook Express have been delivered without any problems - very fast
- e-mails sent from TB are shown as "sent", without any errors,
- recipients do not have my e-mail in SPAM folder,
... but some e-mail have been never received by recipients... the biggest problem is when recipients use Lotus Notes... but not always. Sometimes, even if they use just web site to check e-mails, they do not see mine e-mails...

Where is a problem?
I would be grateful for your help!
THX!