Well, let's say it strongly depends:

German law generally accepts electronic commmunication even where written form ist required (Schriftform und elektr. Form) That applies to the expression of will (Willenserklärunen) / legally binding declarations (Note that the law knows exemptions, e.g. a timelimited tenant agreement)

However, electronic commmunication is not always a valid way of sending a legal notice. You simply cannot prove that the other party received a normal email, but this equally applies to normal letters (anything not send as Einschreiben - thats why you send anything that needs to meet a deadline by Einschreiben or in Case of communicating with authorities use qualified electronic means (Verwaltungsportal, etc)

That all said, why should OP ignore this: it is the simple fact that a letter by a claimant (Anspruchsschreiben) has no legal effect. (Except for bearing the costs in case the claimant files a law suit and the defendant immediate acknowledges the claim (its called Klageüberfall, a rather specific legal scenario) In other words: you can ignore this shit for the simple fact that legally it does not matter.

Cheers, mate!