Rate limits
From ASRG
| Anti-spam technique: Rate limits | |
|---|---|
| Date of first use: | early 2000 |
| Effectiveness: | Low |
| Popularity: | High |
| Difficulty of implementation: | Low |
| Where implemented: | MTA |
| Harm: | Low |
The idea behind rate limit is that usually humans and legitimate mail servers send messages at some limited or small rate. Robots can, sometimes, send bursts of messages. So, the SMTP server shall evaluate the number of connections, per client, over some time window and reject connections, with a temporary reply code, when some threshold is reached. Limits are usually applied to connections, messages or recipients.
Nowadays, rate limiting effectiveness is too low to be considered as a real anti-spam measure, but it remains very effective against DoS and other abuses.
