Version 9 has many issues. How do we reinstall previous version so emails can be sent and received?

Since the install of Version 9, I have been unable to receive emails even after resetting all settings multiple times. Also, cannot not send any message over 2mb of data.

Here is an eMC knowledge base article:

Another option you may want to try before the above:

If you are comfortable executing these steps, give this a try:

(1) Delete any installation files you have downloaded.
(2) Uninstall eM Client, making sure to NOT delete your database directory when asked. This will ensure your settings and data remain in place.
(3) If it exists, delete C:\Program Files (x86)\eM Client
(4) Download and install the latest version from here
(5) The latest version of eM Client should then start with all your data in place.

Was reinstalling with version 8 and this error occurred… MailClient.Storage.Data.DatabaseHasNewerVersionException: Data file ‘C:\Users\randy\AppData\Roaming\eM Client/folders.dat’ has version 7 but only versions up to 3 are supported
at MailClient.Storage.Data.DbRepository1.ThrowIfNewerVersionThanSupported(Int32 dbVersion, String databaseName, String resourceName) at MailClient.Storage.Data.DbRepository1.CheckSchema(String databaseName, String resourceName)
at MailClient.Storage.Data.DbRepository1..ctor(DataStore dataStore, String location, String indexTable, String[] readWriteDatabaseNames, String[] readOnlyDatabaseNames) at MailClient.Storage.Data.DbRepository1…ctor(DataStore dataStore, String location, String indexTable, String[] readWriteDatabaseNames)
at MailClient.Storage.Data.DbFolderRepository…ctor(DataStore dataStore, String dbLocation)
at MailClient.Accounts.ItemRepositories.Open(DataStore dataStore, String accountPath, AccountType accountType)
at MailClient.Accounts.ItemRepositories…ctor(DataStore dataStore, String accountPath, AccountType accountType, String accountName, String protocolName)
at MailClient.DbRepair.ConsistencyChecker.CheckConsistencyForAccount(String accountDirectory, RepairMode mode, CancellationToken token)
at MailClient.DbRepair.ConsistencyChecker.<>c__DisplayClass2_0.b__0(String p)
at MailClient.DbRepair.PerAccountExecutor.Execute(String dataStoreLocation, Func`2 action)
at MailClient.DbRepair.ConsistencyChecker.Check(RepairMode mode, CancellationToken token)
at MailClient.DbRepair.CheckingProcess.Check(CancellationToken token)
AccountType: Mail
DatabaseLocation: C:\Users\randy\AppData\Roaming\eM Client\Archive

This is because you didn’t delete the database.

A version 9 database can’t be used with version 8.

Look at the link @sunriseal gave above, and follow the steps.