Your email attempted to include more recipients than the receiving server allows in a single message. Most servers limit recipients per message to 50-500. Split large recipient lists across multiple messages.
What Does Error 5.5.3 Mean?
Enhanced status code 5.5.3 means you attempted to send an email with more recipients (RCPT TO commands) than the receiving server allows in a single SMTP transaction. Most mail servers impose per-message recipient limits to prevent abuse.
Gmail allows up to 100 recipients per message for external sends. Microsoft 365 allows 500 recipients per message. However, for bulk sending, you should always send to individual recipients or small groups rather than adding hundreds of recipients to a single message. Using individual sends also allows personalization and proper tracking.
Common Causes
- Too many recipients in a single email (To, CC, or BCC)
- Bulk sending script adding too many RCPT TO commands per transaction
- Mailing list software not splitting large lists into batches
How to Fix Error 5.5.3
- Split large recipient lists into batches that comply with the server limit
- Send individual emails to each recipient (preferred for bulk sending)
- Check the receiving server limit (typically 50-500 per message)
- Use proper email marketing tools that handle batching automatically
Frequently Asked Questions
Error 5.5.3 (or 452 4.5.3) means your email included more recipients than the mail server allows in a single message. Every mail server has a maximum recipient limit per message, which includes all To, Cc, and Bcc recipients combined. Microsoft 365 allows up to 500 recipients per message, Gmail limits personal accounts to 500 recipients per day, and other providers have their own thresholds. The message is rejected before delivery to any recipient.
The limit depends on your email provider. Gmail (personal) allows up to 500 recipients per day and per message. Google Workspace allows up to 2,000 per day. Microsoft 365 / Exchange Online allows 500 recipients per message. On-premises Exchange defaults vary and can be configured by the administrator. If you need to reach more recipients, split your list into smaller batches or use a dedicated email marketing platform like Mailchimp or SendGrid that handles batching automatically.
Split your recipient list into smaller groups -- for most providers, keep each batch under 100 recipients per message to be safe. Use BCC for large distributions to avoid exposing all addresses. Space out batches with delays (e.g., 1-2 minutes between sends) to avoid triggering rate limits. For regular large-volume sends, switch to a dedicated bulk email service that manages recipient limits, throttling, and compliance automatically. Server administrators can also increase the MaxRecipientsPerMessage setting if appropriate.
Yes, the recipient limit includes all addresses in To, Cc, and BCC fields combined. Even though BCC recipients are hidden from other recipients, they still count toward the server's per-message recipient limit. A message with 10 To addresses, 5 Cc addresses, and 490 BCC addresses totals 505 recipients and would exceed a 500-recipient limit. Always count all recipient fields when planning large sends.