I am from India. I got Ubunto 12.04 LTS and have recently installed Opera 12.16 through Ubunto software center.
My problem is that the e-mail client provided by Opera does not seem to notify any new messages and sometimes a message like "POP connection failed" occurs.
I have Mozilla Thunderbird (24.05.00) installed by default with my Ubunto package. Is the problem because both these e-mail clients are using the same connection/resources? My Thunderbird always notifies me of latest mails.
Well, if you have two email clients polling the same email server, depending on the frequency they each check for new mail, the times you have set between each check (10 minutes, 1 hour etc) for each program, you may get clashes and overlaps when each program polls the server for new mail. This overlap (if any) will cause one of the programs to issue an error message, because the server is currently busy dealing with the requests from the other program.
To lessen or eliminate this problem, you should either only run one email client at a time or widen the time gap between when the two email clients check the server for new mail.
As for Opera's email client (M2) not notifying you of new mail, that would depend on whether Thunderbird has already received the new mail before M2 has, thus Opera may think it has already been seen (in Thunderbird) and thinks it is not new mail, thus does not notify you. Though I could be slightly wrong here.