In an email to a government official, you might want to sign off with “Mat beschte Gréiss” (with best regards), often abbreviated as “MbG” or “Bescht Gréiss”. Also formal would be “Mat engem schéine Bonjour” (with kind greetings--literally, “with a beautiful hello”). For a more familiar tone, try “Mat léiwe Gréiss” (with kind regards), which you can shorten to “Léif Gréiss”. Or: “E grousse Merci an all Guddes” (a big thank you and all the best).
For formal communications, you might want to end your email with “Sincères salutations” or “Salutations distinguées” (regards). For a less formal but still professional context, try “Cordialement” (sincerely) or “Bien à vous” (warm regards).
“Mit freundlichen Grüßen” (with friendly greetings) is a good one, which you might also find in contracted form: “MfG”. There is also “Mit besten Grüßen” (with kind regards).