How to send emails using PHPMailer and Office 365 SMTP

A detailed PHPMailer tutorial explains how to send email through Microsoft 365 or Office 365 SMTP, emphasizing OAuth2 authentication because Microsoft has largely deprecated basic username-and-password authentication. It covers installing PHPMailer with Composer, registering an Azure Entra ID application, assigning SMTP.SendAsApp permissions, obtaining refresh tokens, and configuring PHPMailer to use the Office 365 SMTP endpoint with TLS on port 587. Practical examples demonstrate sending plain-text and HTML messages, addressing multiple recipients through To, CC, and BCC fields, adding attachments, and embedding images using content IDs, while advising developers to store credentials in environment variables. It also distinguishes Outlook.com SMTP settings from Office 365, outlines troubleshooting for permissions, tokens, connectivity, and spam filtering, and reviews Microsoft limits such as recipient caps, throttling, attachment-size restrictions, and MFA expectations. Finally, it presents Mailtrap as an alternative SMTP and email-delivery platform intended to simplify setup and provide analytics, templates, testing tools, APIs, and support for transactional or bulk email workloads.

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