Change the Default Sending Account in Gmail
To choose a default sending account and email address in Gmail:
New Messages and Forwards vs. Replies
When you compose a new message or forward a message in Gmail, your default email address is used in the From line. Replies work differently. Gmail, by default, uses the address from which you originally sent the message for any replies to it. This makes sense because the sender of the original message automatically receives a reply from the address to which they sent their email, instead of an email address that’s new to them. Gmail lets you change that behavior, though, so the default Gmail address is used in all emails you compose as the automatic choice for the From field.
Change the Default Address for Replies in Gmail
To make Gmail ignore the address to which an email was sent and always use the default address in the From line when you start a reply:
Changing the From Address for a Specific Email
Even when you’ve chosen a different default sending address, you can change the address in the From line on an individual basis. To pick a different From address on a case-by-case basis:
