Give each client a clear route
Use one address or tag per client so every request lands in the right place. Clients should know where to write, and your team should see at a glance whose request it is.
Agree scope and response times
Write down what counts as support and what is billable project work, and how fast you reply to each. It avoids awkward conversations about whether a request is covered.
Keep a record for each client
Store the history, decisions and approvals against the client, not in someone's inbox. When an account manager is away, anyone can pick the thread up.
Separate urgent from routine
Agree what an urgent request is, such as the site being down, and how to reach someone. Everything else can wait for the normal response time.
Report on a regular schedule
Send a short monthly note with what you handled and how long it took. Clients who can see the work are less likely to doubt its value.
Review profitability
Track the time spent per client against what they pay. If one account takes far more support than it earns, change the scope or the price.