Not compatible with SmartFormat v3.0
MailMergeLib v5.8 SmartFormat v3.0 Framework v4.8
MailMergeMessage mmm = new MailMergeMessage("Subject", "Message");
Gets exception "Method not found: 'Void.SmartFormat.SmartFormatter..ctor()'

Correct, MailMergeLib v5.8 references SmartFormat v2.7.2
Then shouldn't nuget dependency be set to SmartFormat.NET = 2.7.2 instead of >= 2.7.2?
Ah, found the issue. Interesting. I think because my app is targeting NET 4.8, it doesn't take lowest version of dependencies since only NET v4.6.1 is in the MailMergeLib dependencies. I created a blank solution targeting Net 4.6.1 and correct dll versions are downloaded.
@Scantheus Today we released a new maintenance version of MailMergeLib (v5.8.2), which is available on NuGet. We included an explicit range of compatible versions for dependencies. Does this for for you, too?
I don't see .NETFramework.Version=v4.8 in the Dependencies.
Tested (and it's a mess to revert back oof). You need NETFramework,Version=v4.8 with the same dependencies you have for v4.6.1. It appears if a framework is not explicitly defined, it will automatically take the latest version of the dependent packages. In this case, it pulls SmartFormat.NET v3.
Couldn't find anything about this behavior here and anywhere else. Thanks again for pointing this out.
Resolved with #38