Growbots allows you to add your email alias as a separate email account.
NOTE: Please remember that sending from an alias will not increase the sending limits set by your email provider. The number of emails sent daily from the original address and the alias should be added and considered as a total number of emails that will be sent from the original email address.
Adding an alias (except Gmail)
Go to Settings → Integrations and click OTHER
Fill out the form as shown below:
Please see this article if you are unsure how to enter your SMTP/IMAP settings.
Note: since Microsoft moved away from using Basic Authentication, Outlook inboxes don't have IMAP available. It's necessary to set up an Office 365 account and connect it using the "Outlook" integration.
Adding Gmail alias
You can add a Gmail alias only when the parent account has 2 Factor Authentication enabled. In this article (Gmail section) you can find the exact instruction how to turn it on and generate special App password, which will be needed to connect the alias.
Your main account firstname.lastname@example.org and it has 2FA turned on.
Go to the Settings, choose Integrations tab and click on Other:
Enter your alias (email@example.com in our case) in the Email field.
Enter your main (parent) email (firstname.lastname@example.org in our case) in the IMAP Username field (please remember that SMTP uses same username and password as IMAP should be checked- just like in the screenshot).
Enter your app password generated by Gmail into the IMAP Password field.
Fill out all other fields as normal:
That's it! Now you are able to send the messages not only from your original account, but also from its aliases.