A list that has not been mailed for six months or more is risky to use as is. Some addresses have died and a few may now be spam traps. Plenty of the people behind the live ones have forgotten who you are.

Sending the full list at full volume is the worst option. Validate first, remove dead addresses, split out the most engaged segment and restart with that.

uChecker's guide to cleaning an email list after a long pause lays out that restart step by step.