All valid mail in ballots are counted. So unless your ballot was incomplete or fraudulence was suspected, it will count as a normal vote.
Possible reasons your ballot might not be valid:
Your signature does not match the one on record with your DMV.
You did not follow the instructions exactly when completing your ballot.
Your ballot was submitted after the deadline.
Mail in ballots have recently been criticized as being more likely to cause voter fraud. In reality, the statistics on mail voting fraud indicate the issue is so infrequent it is not a significant factor in elections.
According to a study done by The Washington Post, only 372 of 14.6 million votes cast by mail in 2016 and 2018 general elections were considered possibly fraudulent. This is a rate of 0.0025% across recent elections.
Additionally, an article posted by former election official Amber McReynolds on The Hill supplies more detailed statistics on voter fraud. In 20 years, over 250 million votes have been cast by mail. Out of these, only 143 have resulted in criminal convictions, indicating a fraud rate of 0.00006% in the past 20 years.
Every state has different rules when it comes to voting by mail, visit your states election office website to determine what applies to you.
Each state has a different deadline for when mail in ballots are due.
Visit here for more information on deadlines: https://www.vote.org/absentee-ballot-deadlines/
Some states allow you access to track your ballot.