I'd argue that it would be outside the scope of that change. The whole card is a parachute to have a quick fix for the problem. Whatever gets raised here, means that we failed in doing whatever we tried to do with emarsys. When we wrote this initially, we did not care too much about these errors, other than logging them in our `registration.mailing_list` module. From our point of view, every error raised by this means the same...

Same goes for testing it - it think the effort needed to write proper tests for this would be far greater than the benefit. (I do understand the point @giftig raised above about tests, but this should be a separate card)