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SMTP 451 4.7.1 - the fifty-emails lesson

LowWordPress sites 1 min readBy Kevin F
TL;DR: A bulk send to ~100 recipients hit WPX's mail throttle: 50 emails per 30 minutes per mailbox. Not a bug - a deliberate guard on a mail service built for correspondence, not campaigns. The lesson the fellowship's mailers keep re-learning since 2023: bulk belongs on a dedicated sender.

Source: WPX ticket #996300, “SMTP Error: [451] 4.7.1” (WPX support portal).

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Kevin F. tried to send a bulk email to around 100 people and got SMTP error 451 4.7.1, resorting to copy-paste batches. Ilona B. at WPX explained the design: 50 emails per 30 minutes per mailbox, an automatic protection for the mail servers’ IP reputation rather than a fault. Exceed it and the mailbox cools off until the window resets.

The guidance matches what this desk has known since the 2023 Tech Com reports (“our digest email continues to grow and is getting clipped”): WPX mail is for day-to-day correspondence. Newsletters, announcements, and anything automated belong on a dedicated email delivery service.

Which is exactly where the digest email landed eventually - and why the Newsletter subdomain exists at all.

Slow mail is a feature; the wrong tool is the bug.