I have not been able to upgrade to a new computer. So I am running an old OS 10.5.8 in a Powerbook Pro 15¨. I recently have had some e-mail problems. I would like to know if this is related with all transitional process from @mac to @icloud.

Nope. just how you have it set up your mail. Check your settings.

First of all, your profile says you are using OSX 10.5.8 which is incompatible wth all features of icloud, although users have been able to use icloud's email with older versions. With the transition to @icloud.com accounts, it's difficult to say what the effect is regarding older versions of OSX. I've read posts by others who are still using these versions and have now been having problems with emails.

iCloud Mail Settings

The link above will take you to Apples settings for your email account, set it up as per instructions.

pvonk wrote:

First of all, your profile says you are using OSX 10.5.8 which is incompatible wth all features of icloud, although users have been able to use icloud's email with older versions. With the transition to @icloud.com accounts, it's difficult to say what the effect is regarding older versions of OSX. I've read posts by others who are still using these versions and have now been having problems with emails.

iCloud mail is a standard Imap account, any version of OSX (or Windows) with an Imap compatible mail client can use it.

This page has illustrated instructions for setting up iCloud Mail in Leopard:

Entering iCloud email settings manually in Snow Leopard or Leopard