It is possible to send automatic email the day of the birthday's contact.
You need to :
- Add a date field YYYY-MM-DD to the contacts, we will call it "birthday"
- Create a segment
- Add a filter on the date field > equal > birthday (write the word)
- Create a new campaign from this segment
Activate the "Allow contacts to restart the campaign" option to allow your contacts to go trough this campaign every year.
You can also improve this campaign by sending the email 1 day, week or month before the anniversary date.
To do that combine 2 relative date filter.
for example if you want to send email to contact 1 week before their birthdate set the filter like this
"birthday" filter equal birthday 1 week