Hello David, aliases and domain aliases should work from MAPI.  You just need to change who you're sending emails from when composing them.  You can also send emails with plus addressing from MAPI.

Larry,

I am guessing unlike the web interface, Outlook will not know to automatically respond using the "to" address?

I most likely with install a trial to fully test everything, but before spending that time, I am trying to do some due diligence first.

Correct, it will not automatically use the TO field when replying to an email.  You would have to change it before sending.

Larry,

I didn't get to installing the latest version with MAPI to test yet, but I just did a quick test with IMAP on our existing install and I remember why we have stuck with webmail and thus haven't been interested in upgrading...

Outlook adds an "on behalf of" header when sending emails where you modify the from email address.  Do you know if this behavior is limited to IMAP and doesn't occur with MAPI?  Alternatively, do you know of a way to prevent Outlook from doing this?

If we have a domain alias of domainb.com for domaina.com, when sending an email from somealias@domainb.com using outlook, a recipient would see the email as from mainaccount@domaina.com on behalf of somealias@domainb.com which obviously partially defeats the purpose of having the alias in the first place.

Hey David, in MAPI you will see the "on behalf of" on the email that's in your 'Sent Items' folder and it's in Outlook only.  If you look at that same email in webmail it does not have that text and it's not in the email header.  The same is true with the email that is received by the recipient (no on behalf of text).

Larry,

Did you confirm that that is true for the recipient in outlook?  Basically, in IMAP, if we send to gmail, on behalf of doesn't appear in the gmail webmail.  If we send to another smartermail domain, it doesn't appear in smartermail webmail, but the moment we download to outlook with IMAP or POP, the on behalf of appears.

For more info on what I think Outlook does...

In looking at the messages, the "From" header is what is entered into the from field in outlook.  Outlook also sets the "sender" header and that is sent to the account that is used in Outlook (root domain name / email as opposed to alias) instead of the from address.  I think smartermail webmail and other webmails/clients ignore the sende header and just display the from as whatever is in the from header, but outlook checks both and if sender and from differ, it displays the on behalf of styling.