You get two types, one is E16 and the other is E2, the E16 gets converted to E2 if you use an AI from what I have gathered.
All estrogen in men is derived from testoesterone via aromatase. E2 (estradiol) gets synthesised first then to E1 which then derives E3 and E4. I believe E1 can also be created in very small quantities via aromatase straight from some adrenal hormones. An AI simply decreases the ability for T to be converted to E (vast majority E2)