Resend event: email.delivery_delayed, a soft bounce, Resend is retrying

TL;DR

Check the subtype when present: MailboxFull, MessageTooLarge, ContentRejected, AttachmentRejected, or General. MessageTooLarge and ContentRejected will not resolve on their own; MailboxFull often will.

Steps

1. Log it against the email_id as a transient state. Common causes: recipient's inbox full, receiving server transient issue.
2. Check the subtype when present: MailboxFull, MessageTooLarge, ContentRejected, AttachmentRejected, or General. MessageTooLarge and ContentRejected will not resolve on their own; MailboxFull often will.
3. Watch, do not act. If it resolves, email.delivered follows. If it does not, email.bounced follows.

When to use

You are seeing this: The email could not be delivered due to a temporary issue. Use this skill when you run into "Resend event: email.delivery_delayed, a soft bounce, Resend is retrying".

When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

Why this happens

The original report does not dig into a root cause. It documents the symptom and the fix that resolved it.

Resend's event reference says email.delivery_delayed occurs whenever the email couldn't be delivered due to a temporary issue, e.g. the recipient's inbox is full or the receiving email server experiences a transient issue. Verified live at https://resend.com/docs/webhooks/event-types. The bounce-subtype table (soft vs hard, MessageTooLarge, ContentRejected, AttachmentRejected, MailboxFull) is documented in the official resend-skills webhooks reference at https://raw.githubusercontent.com/resend/resend-skills/HEAD/skills/resend/references/webhooks.md.