"Tired old hat" may possess a notion of cliché, common place, seen too much. A example is given here for writers (of plots):
you’ve used a plot that’s been done and done again, and that seems
tired (old hat!)
In your context , some consider (so-called "digital natives") that email belongs to the past (of one-to-one marketing). Yet, they might as well:
underestimate its power when combined with CRM, automation and great
Digital natives are opposed to digital immigrants, or sometimes analogue (analog) natives. First emails indeed date from the 1970's. This digital novelty superseded analogue written letters. Since technologies are progressing at a fast pace, old digital now sounds analogue.