SendOptions API needs improvement

[helenktsai]

trafficstars

Issue transferred from internal repo

There are several pain points with the current API that can be improved including:

• It requires use of extension methods instead of properties (e.g. options.SetMessageId(...) instead of options.MessageId = ...) to allow downstream repositories add their own options (e.g. SendToSite)
• There needs to be a way to retrieve configured options
• It's challenging to "stringify" the configured options
• SendOptions can easily be reused in multiple send operations which can easily introduce bugs or undesired behavior
• etc.