How many emails can I send?

A single Mail Merge campaign is limited to 200 contacts. However, users have the ability to create as many campaigns as they wish and (on the Professional Plan) as many followup stages.

Google imposes a limit of 200 emails per day for free Gmail accounts and around 500 emails per day for Google App accounts (actual numbers may vary). If you exceed this number, you risk your account being locked down for 24 hours.

We strongly recommend users to split campaigns and schedule them on different days, which will help you in A/B testing your message while keeping a safe distance from the limit.

But Google allows me to send more than 200... why restrict?

At the time of writing, this page states that you can send up to 2000 emails per day. However, note that the limit provided is for emails sent manually via Gmail's web interface, not for emails sent via APIs or SMTP.

When using Vocus.io, an email is sent via Gmail's SMTP, which is governed by a much lower and dynamic limit.

From observing thousands of users running thousands of email campaigns, we see users being locked out of their Gmail account after sending 200 to 400 emails in a rolling 24-hours window.

We strongly recommend you not exceed 200 emails in a rolling 24-hour window, and in fact seek to increase the gap between campaigns in order to avoid your account being locked by Google.