Email sending limit: external recipients per 24 hours

Microsoft 365 and Google Workspace limit the number of recipients outside your domain your mailboxes may write to each day. Beyond it, they refuse some of the recipients, and may even suspend sending from the mailbox, Outlook or Gmail included. To keep you clear of that block, Nicoka counts the recipients of every mailbox and every domain, and spreads out the sends that would exceed the limit.

What is counted

• Every address in To, Cc or Bcc whose domain is not the mailbox's counts once per email. An email sent to 50 contacts counts as 50, even when they are all in Bcc.
• Internal emails (same domain as the mailbox) do not count.
• The window slides: the last 24 hours count, not the calendar day.

The mailbox limit

It is set in the External recipients max. per 24 h field:

• for a connected mailbox (Microsoft 365 or Google): your profile, Integrations tab, then the mailbox;
• for a mailbox set up over SMTP: in the mailbox edit window.

Empty field (recommended): 3,000 external recipients per 24 hours for a Microsoft or Google mailbox. A freshly connected mailbox starts lower: 25% of that limit the first week, 50% the second, 75% the third. A mailbox sending through another server (Brevo, Mailjet, your host's server) has no limit.

A value you enter replaces this default, warm-up included. Entering 0 is the same as leaving the field empty.

The domain limit

All the Microsoft or Google mailboxes of one domain also share a common limit: 10,000 external recipients per 24 hours by default. Your administrator sets it in Customizing > Admin > Settings, Sending hours block, Email sending limit per sender domain point (empty: 10,000, 0: no limit per domain). Administrators receive an email when the domain reaches 80% of its limit.

When the limit is reached

• Bulk send: the emails that no longer fit are held and go out on their own as soon as the window frees up. The confirmation message says so: « message(s) held by the sending limit, sent from … ».
• Sequence: the step waits for the release time, then the email goes out.
• Single email: it is refused, with the time of the next sending slot. Send it again from that time.
• Email larger than the limit (for example 4,000 recipients for a limit of 3,000): it is not sent. Split it into several sends, or raise the limit.

Choosing the value

• Too low: your campaigns and sequences spread over several days, and single emails are refused on busy days.
• Too high: Microsoft or Google blocks instead of Nicoka. Refused recipients come back as non-delivery reports in your mail client, without showing in Nicoka, and the mailbox may be suspended.
• Nicoka only counts what goes out through Nicoka: emails sent directly from Outlook or Gmail use the same limit at Microsoft or Google. Keep some margin for a mailbox used heavily on both sides.

In most cases, leave the field empty. Only fill it in to raise the limit of a mailbox dedicated to campaigns whose quota at Microsoft or Google you know, or to slow down a mailbox that has already been blocked.

For volume sending, a dedicated emailing tool remains the best option: see Bulk email sending: best practices.