From WP Mail SMTP to PostmanSMTP.

   Recently, I had an email from YAHOO!. Its subject is “Secure your Yahoo account”. I think this is maybe related to “Yahoo hit in worst hack ever, 500 million accounts swiped”. Because …

   I went to “Yahoo Account settings” and turned “Allow apps that use less secure sign in” off. Yahoo mail and Gmail have the same kind option. I don’t use other free mail services. But, I think other famous services have the same option. On Yahoo mail the option default value is ON and on Gmail the option default value is OFF.

   When I turn off the option, I cannot use POP access.
   About IMAP access, I found the difference between Yahoo mail and Gmail. If your email client supports OAuth 2.0, you can access Gmail via your email client, for example Thunderbird, SeaMonkey, etc. Though Yahoo mail itself seems to support OAuth 2.0, it doesn’t accept accesses from PC email client that supports OAuth 2.0. Yahoo mail and Gmail about SMTP connections showed the same behaviors as their POP ones.

   Anyway, I did it. At this point, I had a trouble. I’ve used WP Mail SMTP for a long time, but it gave a send error after turning “Allow apps that use less secure sign in” off. It is not surprising because WP Mail SMTP is one of apps that use less secure sign in. But what can I do to solve the trouble?

   I made a thread on WordPress Support Forum but had no reply. I looked for a suitable plugin by the keywords “mail smtp oauth2”. Postman SMTP Mailer/Email Log looked good. I installed it.

[How to install Postman SMTP with OAuth 2.0 for Gmail]

1. I created a Gmail account for this purpose. If you have an account you don’t care about using for this purpose, you don’t need this step.
2. Install the plugin from WordPress Dashboard.
3. Activate the plugin. If you have Multisite type, do “Network Activate”.
4. Go to Dashboard Home. You can see “Postman is not configured and is mimicking out-of-the-box WordPress email delivery. Email Log | Settings”, and then click “Setting”.
5. About after above, they give us a video like this:
   
6. If you have Multisite type, each child site needs each “Settings”. So, each child site owner can create a suitable settings.