Baking bread with a firm texture that doesn't grow mold
Mold grows on bread because mold spores in the air, or on hands or other surfaces, get transferred to the bread. Bread has plenty of nutrients for these spores to grow.  Mold growth is enhanced by temperatures over 70 degrees F (21C). Humidity and moisture also favor mold growth.
There are a couple of things you can recommend or do to reduce mold growth.
Bread should be handled with clean hands.
Bread should be kept well wrapped.
Refrigeration dramatically slows mold growth.
Freezing virtually stops mold growth.
If not freezing, consume bread as soon as possible.
Margarine and milk help keep the texture soft, and reduce staling.  If you want a firmer texture, you might consider a formula without these ingredients.