In this case, I will actually recommend to send from a shared IP address. Since you are starting with an empty database, your volumes will probably not reach 100.000 emails per month, being the very minimum you need to build and maintain a positive reputation.
There is nothing wrong with starting using a shared IP, and you will be able to migrate the account ...
The limit is 5MB, however when you have the actual file converted into Base64 encoded data, the size of a document increases due to nature of Base64 Encoding and hence you see 3 mb limit.
Moreover you'll see for different types of documents you will have different max file size since the encoding will generate different blob sizes.
Test.stopTest() executes queued anonymous code, then resets the governor limits afterwards. You'll never see things like Limits.getEmailInvocations greater than zero, or other consumed limits. Further, things like "LastRunTime" aren't run until the transaction finalizes, which for a unit test, is after the last line of code executes. Accordingly, ...
This sounds a little more complex than it probably needs to be, but it's the idea that immediately popped to mind. Caveat: I haven't truly thought this through.
assign the SL values into the DE for selection
create an automation that deploys the emails as Step 1
add a WAIT activity for X amount of time
create a query that populates DEs with Open ...
With workflow, process builder, or flow email alert you won't be able to dynamically attach file.
If you are looking for the point and click option only you can check this out. This would install an unmanaged package and you can achieve it using point and click option.
The main problem was with the workflow itself, someone turned on multi currency in our packaging org breaking a lot of workflows since it added the only active currency (USD) to the condition.
And sadly we are also having unrelated problems ("Probably Limit Exceeded or 0 recipients") sending emails in some of the orgs where we clone and modify the ...
Above error message occurs when there a blank email field specified on the recipient list and if the intended user is inactive.
Review resolution steps mentioned on Probably Limit Exceeded or 0 recipients.
Also, There is a Known issue for user lookups unavailable as recipients for email alerts.