You receive multiple copies of the same email message in your email software.
The most common cause of multiple e-mails is configuring your POP client (eg. Outlook, Apple Mail) to leave copies of your e-mail on the mail server.
Every time your e-mail program checks for new messages it makes a connection to your mail server and has look at what is there and compares it to what you already have on your computer. After it does this, it is supposed to download only the new messages. However, if the mail headers stored on your computer become malformed or corrupt your mail program does not know you already have the message and downloads it again.
Before checking your email via your POP client, log into your e-mail using Ecenica webmail. If you only see one copy of the message in Webmail but you see multiple copies in your e-mail program you can be sure that the problem is with your mail program.
The quick fix for this is to change the setting that causes your mail program to leave a copy of mail on the server.