A spam bot or abusive user may flood the helpdesk with a large number of emails and create lots of unwanted tickets or messages within tickets.
Deskpro prevents this sort of abuse by limiting the maximum number of emails a person can send in a short period.
You can set the limit at Admin > Setup > Email Rate Limiting. The default is that after 15 emails within 10 minutes, the helpdesk will reject incoming emails for 15 minutes.
An email will be sent to the user warning them when they reach the limit. The user will still be able to reply through the portal.
Emails rejected by rate-limiting are saved in a rejected state at the Incoming Email log (at Admin > Tickets > Email Accounts).
From there, you can choose to re-process a rejected email and make it into a new ticket or a ticket reply.
This limit does not apply to email replies from agents.