When does the Mail API per-process limit of 200 emails come into play with my customization(s)?

Environment:

Connect for PHP (CPHP) API, Process Designer, Custom Process Model (CPM) / Service Process Model (SPM)
All product versions

Resolution:

The 200 email recipient limitation described in the CPHP technical documentation is on a per-process basis. If you use CPHP exception handling in your code you should see this indicated in the API response exception when the API call fails. Regardless of the source of problem(s) encountered with the API, the use of proper exception handling within the code should determine the source of the problem. For further details please see

Answer ID 9640: Connect for PHP Best Practices and Gotchas
 
In terms of the limitation being per-process - this can come into play only if the script sending emails is sending to a total of over 200 recipients (including to and cc addresses) or if a single process is calling a script (or multiple scripts) multiple times and the resulting addition of all email recipients is over 200. For example, this can come into play with asynchronous CPM customizations, because asynchronous CPM scripts are called by a utility process that runs multiple queued 'script runs'.
 
That said, the mail API is intended for use cases not supported by the use of Message Templates. This includes emailing from scripts in situations where there is an error, to notify someone to take a look. For further details see

Answer ID 12321:  Sending emails from PHP Customizations using the Mail API

Answer ID 5380: Customizing notifications and email messages sent by Oracle B2C Service