Support high outbound mail volumes

Scenario

When using cloud providers for sending mail, there are inherent limits to sending mail.

• Gmail : https://support.google.com/a/answer/166852?hl=en

  • 2000 msg per day

  • 10K total recipients per day

  • 3000 unique recipients per day

These rates can change without notice, so JEMHC does not ‘try’ to stay within them. If JEMHC sends mail volumes that hit this limit, the mail-server can block the mail sending account. JEMHC reacts to send-failures by backing of in ever increasing amounts. After an hour, JEMHC takes the handler offline which re-enabled manually.

Options

Future implementation of https://thepluginpeople.atlassian.net/browse/JEMHC-2415 could allow the load to be spread over a set of accounts.

Use of SMTP relay features of some mail servers (Gmail: https://support.google.com/a/answer/2956491#sendinglimitsforrelay ) has a combination of limits (see link for full details)

• The maximum number of messages a user can send in a 24-hour period is 10,000. However, this can vary, depending on the number of user licenses in your Google Workspace account.

• A registered Google Workspace user can't relay messages to more than 10,000 unique recipients in a 24-hour period. 

The maximum number of total recipients allowed per customer per 24-hour period is approximately 130 times the number of user licenses in your Google Workspace account, with an upper bound of 4,600,000 recipients per 24-hour period for large customers. If a customer exceeds this limit, users see the error "550 5.7.1 Daily SMTP relay limit exceeded for customer."