The most common salutations used in emails for seniors are: "Sir" for a male senior, "Ma, "Ma'am or "Madam" for a female senior.
Some seniors also like to be addressed as "Mr" for Male seniors and "Ms" or "Mrs". It is best you find out what works for this person in order not to offend the person when you send them an email.
In most cases, the first salutations listed above are widely accepted by many.
Let us say that you have to send emails to seniors. How are you going to pull that off properly? It can be a bit complicated but these are some of the salutations that you can use so that the seniors will not get offended. You can use sir for male seniors and you can use ma’am or madam for female seniors.
Take note that some seniors would still insist to be called Ms. or Mrs. You need to get to know the person that you will be sending the email to so you can be sure.