feat req: considering change the dovecrak and eximload to courier suite

[mckaygerhard]

considering changing the mail back end to one more robust

myvesta currently uses a couple of mail solution back end.. but maybe is better to use the Courier suite. that is far away more secure and optimized

PROS

• 100% most open source secured mail suite
• Maildir enhanced mail storage vs the current mbox ?
• configuration its 100% directory+files..
• you can setup each per site per user configuration using a isolated file for each value inclusivelly

CONS

• source code of myvesta will need too much changes
• workflow of the myvesta will need to change specially in the dkim