Fix "421 4.7.0": The server is temporarily deferring your mail (try again later)

If your email is bouncing with 421 4.7.0, it means the server is temporarily deferring your mail (try again later). Here is exactly what causes it and how to fix it.

What 421 4.7.0 means

421 4.7.0 is a temporary deferral, not a permanent failure. The receiver is throttling you because of sending-rate or reputation concerns, and expects your server to retry later.

How to fix 421 4.7.0

• Slow your send rate and reduce concurrent connections.
• Improve IP/domain reputation with warm-up and clean lists.
• Ensure your server honors retry backoff instead of hammering the receiver.

How Rainmail helps

Rainmail sends from your own domain on a dedicated, isolated IP with SPF, DKIM, DMARC, reverse-DNS and managed warm-up handled for you, plus an AI that watches your list health and deliverability. It also welcomes the senders Amazon SES, SendGrid and Mailchimp reject — from $8, cheaper per email than SES. Run the free 10-second checker or see plans.