Rate Limiting/Retry mechanism for short-term errors

[ben-z]

SMTP providers usually have (short-term) rate limits (e.g. can't send more than 20 emails per second). Add an option to support this. The GitHub provider achieves this by using a custom centralized transport.

[ben-z]

Can simply use a mutex, a last-sent timestamp, and a sleep to achieve this. The parameter can be the minimum time between requests.

[ben-z]

Alternatively we can implement error handling for errors like 421. This happens when I try to send 20 emails at once using a gmail SMTP server:

╷
│ Error: 421 4.3.0 Temporary System Problem. Try again later (10). For more information,
│ 4.3.0 go to
│ 4.3.0  https://support.google.com/a/answer/3221692 bj19-20020a05620a191300b00790afc26983sm61858qkb.72 - gsmtp
│
│   with email_email.all_emails["REDACTED"],
│   on main.tf line 49, in resource "email_email" "all_emails":
│   49: resource "email_email" "all_emails" {
│

https://chat.openai.com/share/96fe4067-6bc9-4696-add3-e8788e07aea3

All 4xx SMTP errors are retriable:
https://apps.google.com/supportwidget/articlehome?article_url=https://support.google.com/a/answer/3221692&assistant_id=generic-unu&product_context=3221692&product_name=UnuFlow&trigger_context=a

[ben-z]

Solved by #2 (comment)