The length of the 'messageid' attribute of the 'email' entity exceeded the maximum allowed length of '100'

I was receiving this error often at the Event Viewer > Application Log of the CRM Server.

#9628 – An error occurred while delivering the e-mail message with subject "This is a second demo" in mailbox crmdemo@gmail.com for delivery to http://192.168.1.205:5555/crmdemo.System.Web.Services.Protocols.SoapException: Server was unable to process request.
at System.Web.Services.Protocols.SoapHttpClientProtocol.ReadResponse(SoapClientMessage message, WebResponse response, Stream responseStream, Boolean asyncCall)
at System.Web.Services.Protocols.SoapHttpClientProtocol.Invoke(String methodName, Object[] parameters)
at Microsoft.Crm.Sdk.Proxy.CrmService.Execute(Request Request)
at Microsoft.Crm.Tools.Email.Providers.CrmPollingMailboxProvider.DeliverMessageInternal(EmailMessage emailMessage)
at Microsoft.Crm.Tools.Email.Providers.Pop3PollingMailboxProvider.DeliverMessageInternal(EmailMessage emailMessage)
at Microsoft.Crm.Tools.Email.Providers.CrmPollingMailboxProvider.DeliverMessage(EmailMessage emailMessage)
at Microsoft.Crm.Tools.Email.Providers.CrmPollingMailboxProvider.Run()\r\n
0x80044331
A validation error occurred. The length of the 'messageid' attribute of the 'email' entity exceeded the maximum allowed length of '100'.
Resolution:
Tweak the Message ID attributes Maximum Length from 100 - 200 or 250 and you are good to go.
Procedure:

1. Settings > Customizations > Customize Entities > Email > Attributes
2. Double click Message ID and change the Maximum Length
3. Save and Close
4. Publish