Changes

You will notice that there is really very little difference in the code used for static mail and dynamic mail.  The class that supports dynamic mail has a private dictionary collection for holding on to any mail content waiting to be injected.  It could have been made public to allow mail to be added directly into the collection, but that is not good practice.  Instead a public Add method was provided so that mail could be sent, so to speak, to the collection.  This code is for a specific MOD, not a robust framework, so it isn't overly concerned with error handling. You can improve that based on your needs.

You will notice that there is really very little difference in the code used for static mail and dynamic mail.  The class that supports dynamic mail has a private dictionary collection for holding on to any mail content waiting to be injected.  It could have been made public to allow mail to be added directly into the collection, but that is not good practice.  Instead a public Add method was provided so that mail could be sent, so to speak, to the collection.  This code is for a specific MOD, not a robust framework, so it isn't overly concerned with error handling. You can improve that based on your needs.

Notice the additional code in the Edit method, where any mail in the dynamicMail collection is injected into Stardew Valley's content.  There will be no mail in the dynamicMail collection when the MOD is loaded (in this case) the first time.  If you add mail after the original load, then the content will have to be reloaded by invalidating the cache.  Refer to [https://stardewvalleywiki.com/Modding:Modder_Guide/APIs/Content#Advanced Invalidating Cache] for more details.

Notice the additional code in the Edit method, where any mail in the dynamicMail collection is injected into Stardew Valley's content.  There will be no mail in the dynamicMail collection when the MOD is loaded (in this case) the first time.  If you add mail after the original load, then the content will have to be reloaded by invalidating the cache.  Refer to [[Modding:Modder_Guide/APIs/Content#Cache invalidation|Cache invalidation]] for more details.

===Send a letter (using dynamic content)===

===Send a letter (using dynamic content)===