Three things, in practice.
Bilingual emails are a choice
Private businesses are not required to email in Welsh, but some Welsh brands find a bilingual subject line or greeting suits their audience. If you do it, do it consistently. I write in English, so any Welsh copy should come from you or a translator.
The rugby calendar moves products
The Six Nations in February and March, and the autumn internationals, lift anything red, anything for match day and anything giftable. Plan them in rather than reacting on the day.
St David’s Day is a real moment
1 March gives Welsh food, drink, gift and homeware brands a strong reason to email, and it sits close enough to Mother’s Day that the two can be planned together.