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4 articles tagged with SMTP ports.
A timeout tells you where the SMTP conversation stopped, and that narrows the cause fast. Here are the timeout stages, the four root causes worth checking, a ten-minute diagnostic sequence, and the production patterns that prevent recurrence.
SMTP AUTH proves your client may send; SPF and DKIM prove your message is genuine. This guide compares PLAIN, LOGIN, CRAM-MD5, SCRAM, and XOAUTH2, walks the handshake step by step, maps ports to encryption modes, and decodes the errors you will actually hit.
An email API POSTs JSON over HTTPS; SMTP relay runs a multi-step protocol conversation on port 587. This guide compares the two on latency, batching, error handling, templates, and vendor lock-in, includes a full port reference table, and shows the hybrid setup most teams actually end up running.
SMTP uses ports 25, 465, 587, and 2525. Here's what each port does, how they handle encryption, and which one to use when sending email.
