Exocrine glands are classified as merocrine, apocrine and holocrine, depending on their mode of secretion. All these are able to discharge their products via duct system.
All enzyme secreting glands of GI tract or pancreatic acini are merocrine type. No part of secretory cell is lost during secretion which takes place by exocytosis.
Mammary glands, which secrete milk, are apocrine type. Apical end of the cells accumulate secretory material and cell apex gets pinched off to release the product.
Sebum secreting sebaceous glands on facial skin are holocrine type. Secretory cell with its product gets dislodged from basal membrane and cells are regularly lost inside the gland producing sebum.
In the image A is holocrine type, B is merocrine type and C is apocrine type gland.