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Transactional Email & SMTP
Getting a site's own mail delivered — password resets, order receipts, form notifications. PHP mail() from a shared IP lands in spam, so hosts and site owners route through an authenticated relay instead. Distinct from the mailbox hosting in the Email layer.
Products in this layer
Market Share →
Switching cost. Deliverability reputation builds on the sending domain and IP; switching relays resets warm-up and risks a spam-folder window.