Thanks for your quick reply.
I plugged in my laptop computer in my dorm. And the "From" address appeared as "email@example.com". So when I sent any mail to hotmail or gmail account, PINE worked pretty well. However when I replied back, I got the following message:
This is an automatically generated Delivery Status Notification.
THIS IS A WARNING MESSAGE ONLY.
YOU DO NOT NEED TO RESEND YOUR MESSAGE.
Delivery to the following recipients has been delayed.
When I clicked "SETUP --> CONFIG", the following info was shown. I did not change anything in the .pinerc file.
personal-name = <No Value Set: using "yzhua3">
user-domain = <No Value Set>
smtp-server = <No Value Set>
nntp-server = <No Value Set>
inbox-path = inbox
incoming-archive-folders = <No Value Set>
pruned-folders = <No Value Set>
default-fcc = <No Value Set: using "sent-mail">
default-saved-msg-folder = <No Value Set: using "saved-messages">
postponed-folder = <No Value Set: using "postponed-msgs">
read-message-folder = <No Value Set>
form-letter-folder = <No Value Set>
literal-signature = <No Value Set>
signature-file = <No Value Set: using ".signature">
I really do not know the reason for this. I am still quite new at Ubuntu and PINE. I really appreciate it if you can give me some hints to solve it.