A common issue with WordPress is failure to reliably send email. WordPress relies on the PHP 'mail()' function to send emails. In the fight against spam, most email servers require that the emails they receive are legitimate. This involves a number of checks on your domain and the email itself to confirm it's a real email. The more checks that fail, the more likely your email will be flagged as spam or even rejected by the receiving mail server.
So, if you use the web server to send your emails, they will more than likely be blocked, and your domain may also become blacklisted.
The simplest solution is to connect WordPress to your actual mail server. You do this by authenticating on of email accounts via a protocol called SMTP. There are many free and premium SMTP plugins for WordPress that will help you set this up. SMTP servers use proper authentication to make sure that email is sent by an authorised sender. This improves deliverability, and your emails safely land in users’ inboxes. It provides higher security and deliverability than the default Hypertext Preprocessor (PHP) `mail()` function.
On December 31, 2022, Microsoft blocked basic authentication to SMTP. This means you cannot connect your WordPress website to your Microsoft 365 email account using SMTP. So how do you connect your WordPress website to Microsoft 365, so your website can reliably send emails? Thankfully there are a number of plugins that will help. Most of them require a "pro" or premium license though.
However, there is an excellent plugin called FluentSMTP. It's 100% free and they have a great article that not only explains the issue further but also takes you through installing and setting up your WordPress website to connect to Microsoft 365. Once connected you will have improved the deliverability and security of your emails.
Read the article here: How to Send WordPress Emails with Microsoft 365
