The primary reason created email boxes don't work is that part of the creation process was skipped or wrong mail settings are being used.  If you can see your mailbox in your Plesk control panel, but it's not working in an email program or Webmail, check the following things.

1) Make sure the Mailbox option was checked when the mailbox was created.  Even if the mail name was created, if no option was selected, the mail name won't do anything.  It must be designated as either a mailbox, a mail forward, or a mail group to work.

A mailbox is a true email box with send and receive ability.  A mailbox must be setup in an email program (like Outlook Express) or accessed through our Webmail interface to be used. A mail forward is not an email box.  It is simply a redirect for the mail.  A mail forward sends any mail received by that mail name to another mailbox which you selected when you created the mail forward. A mail group is basically a mail forward to more than one address.  For example if you have a sales mail name on your domain and you'd like that mail forwarded to each of your salespeople you could enter all their email addresses into the mail group for sales.  All email sent to sales@yourdomain.com would then be automatically forwarded out to the members of the mail group.  (Keep in mind that this function is not intended for use for spam mail or running mailing lists.  Such uses would be a violation of our terms of service and would result in immediate suspension of your account.)

2) Make sure that the mail name was not set up as a forward or mail group.  Forwarded mail (which includes mail groups) is forwarded directly out to the designated receipient.  It does not sit on the server and cannot be retrieved using the mail name setup here.  Forwarded mail can only be retrieved through the email address it was forwarded to.  For example if you create a mail name of info and set it to forward to you@aol.com, when that mail comes into our server it is routed to the info mail forward which immediately sends it out to the you@aol.com email address.  You would then receive this mail by logging on to your AOL account and retrieving mail through their system.

3) Make sure that all mail settings you are designating in your email program setup or Webmail login attempt are correct.  The userid and password for a mail login are not the same as those used to access your hosting space.  They are the settings designated when you created the mail name through the control panel.  The userid is the mail name you created and the password is the password you set when you created the mail name. 

Also check your mail servers.  They are yourdomainhere.com both incoming and outgoing.  Ex. if your domain were bobnrob.com your mailservers would be bobnrob.com for both incoming and outgoing mail servers.

Lastly, check the case you are using.  If you set the mail name up as laura, but are using a userid of Laura, the computer will not match and will say your userid is invalid.  Rule of thumb is to use all lowercase letters in an email address.  Spaces and other characters should not be used.  Stick to . or _ if you must create a break in the address.