How to properly configure SMTP on a WordPress site and send emails from different emails?

Question

SMTP

There is a site (wordpress), which has different forms for collecting client applications for participation in various contests, promotions, bonus programs.
The site has a plugin installed - Ninja Forms, through which all forms are implemented. Until recently, there were no problems, but now customers have stopped receiving notification letters to the gmail mail client.
Ninja forms made it possible to send notifications to clients from different mailboxes (or rather, not send them from different mailboxes, but visually substitute these different mailboxes in client letters in the "from" field).
That is, for example, a client sends an application for participation in the competition, he receives a notification letter in the mail. When he opened the email, the "from" field was filled with the corresponding "[email protected]" mailbox. If the client sends an application for participation in the bonus program, in his letter in the "from" field was put the box "[email protected]".
Those. a box was substituted, which belonged to a certain subject of forms.
All mail was sent by a standard WordPress mailer, but after the problem arose, it was decided to enable SMTP so that letters would normally come to clients on all mail clients.
After connecting SMTP from Google, letters began to arrive normally again, but there was a problem that now in all letters in the "from" field only one specific box is substituted, to which Google's SMTP was configured. And it is necessary that it would be as before, depending on the form that the client filled out, the corresponding mailbox was substituted in his notification letter.
Can you please tell me how to solve this problem and show different boxes depending on the subject of the submitted form?

Answer 1

Sending from the required addresses must be allowed in the account settings. Gmail entries: https://support.google.com/mail/answer/22370?hl=ru
Before that, in order to confirm ownership of these addresses, incoming mail must be forwarded to an available valid mailbox (or to a specially configured webhook) , you can use the same Gmail address.

Answer 2

Use any email service: Sendgrid, Mailgun, Mailjet..