In case the customer keeps purchasing a lot of things from you then it can be a possibility
that you send out mails to inform them about new products in a similar category of purchased products. It is also important to let your subscriber have an idea regarding the number of emails they will receive in a certain period. This is the differentiating factor between regular emails and occasional ones. Occasional commercial mails should not be sent in a frequent manner. There can be a situation where your customer will be fed up of your daily mails and opt out of the mailing list in a quick manner.