Email limits
The message size, recipient, mailbox and retention limits that apply to your email service.
Message size
The largest message the system accepts is 50MB, including all attachments.
Recipients on a single message
One message may address at most 100 recipients across the To, CC and BCC fields. A distribution list held in Zimbra counts as a single recipient, however many people it reaches.
Our smart hosts work through the recipients in order. Where a message carries more than 100, they deliver to the first 100 addresses and then reject the message back to the sender.
This matters when you resend. Remove the first 100 recipients before trying again and bring the total to 100 or fewer, or everyone who already received the message gets a second copy.
For regular mailings to large lists, see sending a newsletter.
Outgoing rate limits
Everyone sending outgoing mail through the service is subject to rate limits. Three separate limits apply.
| Limit | What it counts |
|---|---|
| IP address recipient limit | The number of recipients the system accepts for delivery from a single IP address, whether that address is a home computer or a server. |
| Domain sending limit | The number of recipients allowed from a single domain. |
| Single user limit | The number of recipients one authenticated SMTP user can send to in a rolling hour. |
Each limit is set at one of four levels: Low, Normal, High and Very High. Which level applies comes from the product you bought, so check your commercial terms. The exact figures are in the control panel, in the support section for your mail domain.
The single user limit is the one that catches organisations out. Where an Exchange server, or anything like it, sends outbound mail through the service using SMTP authentication, everything it sends counts against that one limit. At the Low and Normal levels a busy server reaches it quickly, and the answer is a package carrying the High limit or above.
Mailbox size
The maximum mailbox size depends on the type of mailbox you have. Your email administrator can tell you which applies to yours.
Zimbra Connector for Outlook keeps its local copy in its own ZDB file rather than a PST, so the size limits that affect PST files do not apply.
How many mailboxes an administrator can create
A domain administrator can create mailboxes without any further check. To cap that, send a support request naming the domain and the maximum number of mailboxes the administrator should be able to create.
Trash and quarantine retention
Items in your Trash folder are not deleted automatically. Emptying Trash on a schedule can be turned on, but only if you or your email administrator ask for it.
Quarantined messages are removed automatically after 16 days.