Outbound sending limits
ITProMail applies outbound limits to every account to protect sending reputation and to keep spam from being sent through the service. These are the published limits. Plan sends around them rather than discovering them when a message is refused.
The limits
| Limit | Value | Notes |
|---|---|---|
| Recipients per hour | 300 | Counted per recipient address. |
| Recipients per day | 1000 | Counted per recipient address. |
| Message size | 50 MB | Includes headers and attachments. |
Recipients are counted per address. A single message to 40 addresses uses 40 of your hourly allowance, and Bcc does not change this. Both the hourly and daily limits apply at the same time.
Message size and attachments
The 50 MB limit applies to the whole message as sent. Attachments are base64-encoded in MIME, which adds roughly a third to their size. A limit of 50 MB therefore allows about 36 MB of raw attachment data, before accounting for the message text. If you need to send larger files, share a link instead of attaching them.
What happens when a limit is reached
When a send would exceed a limit, the server refuses it during the SMTP transaction and returns an error reply. Your mail client should show a failed send. Read the reply code and text, because they tell you which limit applied, and the same error can have different causes. For the meaning of common codes, see reading bounce messages and SMTP codes.
The steps that follow from this:
- Stop any automatic retry loop in your client or script. Retrying at once keeps you at the limit.
- Wait for the window to pass before resending. Do not assume it resets at a fixed clock time.
- Check which recipients received the message before you resend the batch. Resending to people who already received it creates duplicates.
Staying under the limits
- Spread large sends across hours. A list of 1000 recipients needs at least four hours at the hourly limit, and it must fit within the daily limit as well. Send in batches of 250 or fewer per hour to leave room for other mail.
- Keep lists clean. Remove addresses that return permanent 5xx bounces. Repeated sends to dead addresses hurt reputation and use up allowance. See bounce messages.
- Use one message per recipient when content is personal. This avoids exposing other recipients, and it still counts once per address.
- Keep messages small. Large attachments are the most common cause of size refusals.
Need more capacity
If your use case regularly exceeds these limits, contact support@itpromail.com before you start sending. Describe the volume, the type of mail and the recipients. The limits in this article are the ones that apply to all accounts.