How it works
Each email sent from Bitrix24 Email Campaign has Unsubscribe & Report Spam options.
In Bitrix24 there is an internal email campaign spam system rating that depends on the number of received spam reports. This means, if your email campaigns result in a big number of spam reports from recipients - the number of email messages available for your Bitrix24 will be restricted or even blocked.
If the number of emails sent from your Bitrix24 is growing with no spam reports from recipients, then the number of email messages you can send from your Bitrix24 will be growing.
How to increase the daily limit
For example, your daily limit is 1'000 emails. But your monthly limit is 1'000'000 emails (1'000'000/30=3'333).
To increase the daily limit, you need to create a campaign with 1'500 emails. 1'000 emails will be sent, 500 will be added to the queue. The limit will be increased the next day and these 500 emails will be sent. So, to increase the daily limit, you need to exceed the current limit.