Is an email alias technically the same as a forwarding internally?

Solution 1:

Both an alias and a forward effectively do the same, they redirect mail for local recipients.

In the old days a "forward" was configured by the user by placing a ~/.forward file in their home directory. Mail gets forwarded from a mailbox, with or without leaving copy of the forwarded message in the original mailbox.

In contrast an "alias" was configured by a server administrator in for example the systemwide /etc/aliases file. There is no actual mailbox for the alias address, any email received for an alias is going to be delivered to one or more other email recipients.

Control panels, sieve rules, virtual mailboxes and other innovations have blurred the lines considerably and I don't think most people really make the distinction on the span of control mentioned above.

At which step that redirect happens depends on the exact mail server and redirecting mechanism selected.
Postfix for example has several forms of address rewriting in addition to the ~/.forward and /etc/aliases files that all happen at different stages and will all have widely/subtly different effects: http://www.postfix.org/ADDRESS_REWRITING_README.html

What exact method you choose may have impact om where other delivery steps such as anti-spam and antivirus filtering will happen, on the original address, on the destination mailbox, or both.

AFAIK The problem associated with redirecting mail messages is primarily when the target of that redirect is not on the same mail server, i.e. when you redirect messages for [email protected] to [email protected]