Both a user name and an email are required, however they do not need to be the same. You can choose to login using either, and you are allowed to change emails but not user names.
So, if users are registering with the same email for both this is the possibility however the login should still work with either. On a side note, if the users are having emails blocked it is not likely due to their entered email. This would suggest something else that is flagging your emails are “spam” even though they aren’t. Some possibilities are that the domain and sending email are not the same, or possibly the service you use to send them. Having the emails sending now might just mean they used a more forgiving email client but that isn’t really solving the problem
Thank you for your quick response. It only works with the email address which I changed. When I try signing in with my client’s username which is her main email address it provides a message Incorrect Password, so it definitely does not work with both. Is this a bug within WordPress? I checked the domain name of the sending email, and it also is definitely the same and correct. I have spent days with with the email provider comcast.net and they thought it may be blocked at a server level meaning no comcast.net clients should be getting emails from my website. In checking with my other clients using a comcast.net email address they are all receiving my websites emails using my domain name. Any additional thoughts are welcome. Again, thanks for your help!
I tried to replicate exactly what you are doing here with the users and cannot reproduce it (WordPress 6.8.3, without any plugins & with standard theme). A user with an email address test1@example.com and a username test2@example.com can log in to the backend without any problems using both details.
The login process can be influenced by plugins. Make sure you don’t have any plugins that interfere with this. Security plugins are a possibility, but so are plugins that actually only change the login details—there are some that allow you to force the user to enter only their username or only their email address. Check this carefully.
Also check under Tools > Site Health to see if WordPress itself reports any anomalies here.
Furthermore, a note about your email problem: this definitely indicates a misconfiguration on your part. My recommendation would be to install an SMTP plugin that shows you possible problems. Take https://wordpress.org/plugins/wp-mail-smtp/, for example. After installation and activation, go to WP Mail SMTP > Tools and send a test email to yourself. The plugin should report any technical problems, such as a missing, incorrect, or non-existent SMTP entry. In general, I would recommend using authenticated SMTP for all emails, as this is now a requirement for many email service providers for incoming emails.
