You should send marketing emails as often as you can without annoying your audience.
Segment your list to ensure you are sending the right message to the right people and then watch your open rates. If people stop opening your emails, then it might be necessary to reduce the frequency in which you send them.
The key is watch metrics and see how your audience responds. If your company has a useful offer that can be promoted daily, that’s great! However, quarterly or monthly eNewsletters are sufficient for most companies outside of their lead capture email drip campaigns emails.