When you send an email using an alias address, Mixmax allows you to continue using your alias even after your recipient replies. Here are the steps to take if you always want to reply from the alias the email was sent to:
The default reply controls are in your Gmail settings. From Gmail, first, click the Settings (gear) icon in the upper-right corner of the page:
Next, click the Accounts and Import tab and make the change under the When replying to a message setting. After that, click the Import Email Addresses to Mixmax button, and you'll be all set!
Sending an email using an alias with Outlook is not currently supported by Mixmax.
FAQ
Can replies to my emails go to a different address?
Replies always come back to the address you sent from. Mixmax doesn't have a separate Reply-To field, but you can get replies in another inbox too:
Forward them automatically: in Gmail, set up automatic forwarding to the other address, or create a filter to forward only some emails. Replies still reach your inbox first, so Mixmax tracks them and stops follow-up stages as usual.
CC the other address: it gets a copy of your email, and of any reply where the recipient clicks Reply all.