Hi Aamer - thank you for your response.
I have this from the Alert in Email Server Profile:
Email Server Error Code: Smtp server returned GeneralOutgoingEmailServerError GeneralFailure exception.
And from the log error in mailbox details:
Mailbox Async Processing State
mailboxid : f3ab3f14-583c-e611-80e3-5065f38b6601
hostid: Null
processingstatecode : 0
processinglastattemptedon : 4/26/2018 11:36:26 AM
Mailbox Synchronization Methods (2 is server-side sync or email router, 1 is Outlook sync, 0 is none)
incomingemaildeliverymethod : None
outgoingemaildeliverymethod : EmailRouter
actdeliverymethod : OutlookClient
Mailbox Enabled State
enabledforincomingemail : False
enabledforoutgoingemail : True
enabledforact : False
Mailbox Idle State (shows how many times the mailbox was processed with no email items or Appointments, Contacts and Tasks to synchronize)
noemailcount : 0
noactcount : 0
Mailbox Backoff Parameters (shows when the mailbox is scheduled to process next time)
postponemailboxprocessinguntil : 12/31/9999 11:59:59 PM
postponesendinguntil : 4/26/2018 12:15:00 PM
receivingpostponeduntil : 2/27/2018 10:14:41 AM
receivingpostponeduntilforact : 1/1/1900 12:00:00 AM
Mailbox Test and Enable Parameters
testemailconfigurationscheduled : False
testemailconfigurationretrycount : 0
testmailboxaccesscompletedon : 4/26/2018 11:36:23 AM
postponetestemailconfigurationuntil : 4/26/2018 11:41:23 AM
Mailbox Last Sync Cycle Information
lastsuccessfulsynccompletedon : 4/26/2018 11:36:26 AM
lastsyncerror : ActivityId: f3ab3f14-583c-e611-80e3-5065f38b6601
>Error : System.Net.Mail.SmtpException: The server committed a protocol violation The server response was:
at System.Net.Mail.SendMailAsyncResult.End(IAsyncResult result)
at System.Net.Mail.SmtpClient.SendMailCallback(IAsyncResult result)
lastsyncerrorcode : 28
lastsyncerrorcount : 1
lastsyncerroroccurredon : 4/26/2018 12:10:00 PM
itemsprocessedforlastsync : 0
itemsfailedforlastsync : 0
Email Server Profile Details
Email Server Profile General Settings (servertype: 1 is others, 0 is Exchange)
servertype : 1
useautodiscover : False
maxconcurrentconnections : 108
minpollingintervalinminutes : 1
Email Server Profile Incoming Email Settings
incomingauthenticationprotocol : Basic
incomingcredentialretrieval : UserSpecified
incominguseimpersonation : False
incomingusessl : True
incomingportnumber : 995
Email Server Profile Outgoing Email Settings
outgoingauthenticationprotocol : Basic
outgoingcredentialretrieval : UserSpecified
outgoinguseimpersonation : False
outgoingusessl : True
outgoingportnumber : 587
Recent Trace Log details
tracecode : 28
errortypedisplay : GeneralOutgoingEmailServerError
errordetails : ActivityId: f3ab3f14-583c-e611-80e3-5065f38b6601
>Error : System.Net.Mail.SmtpException: The server committed a protocol violation The server response was:
at System.Net.Mail.SendMailAsyncResult.End(IAsyncResult result)
at System.Net.Mail.SmtpClient.SendMailCallback(IAsyncResult result)
collationlevel : 0
modifiedon : 4/26/2018 12:10:00 PM
tracecode : 28
errortypedisplay : GeneralOutgoingEmailServerError
errordetails : ActivityId: f3ab3f14-583c-e611-80e3-5065f38b6601
>Error : System.Net.Mail.SmtpException: The server committed a protocol violation The server response was:
at System.Net.Mail.SendMailAsyncResult.End(IAsyncResult result)
at System.Net.Mail.SmtpClient.SendMailCallback(IAsyncResult result)
collationlevel : 0
modifiedon : 4/26/2018 12:10:00 PM
tracecode : 28
errortypedisplay : GeneralOutgoingEmailServerError
errordetails : ActivityId: f3ab3f14-583c-e611-80e3-5065f38b6601
>Error : System.Net.Mail.SmtpException: The server committed a protocol violation The server response was:
at System.Net.Mail.SendMailAsyncResult.End(IAsyncResult result)
at System.Net.Mail.SmtpClient.SendMailCallback(IAsyncResult result)
collationlevel : 0
modifiedon : 4/26/2018 12:09:59 PM
tracecode : 28
errortypedisplay : GeneralOutgoingEmailServerError
errordetails : ActivityId: f3ab3f14-583c-e611-80e3-5065f38b6601
>Error : System.Net.Mail.SmtpException: The server committed a protocol violation The server response was:
at System.Net.Mail.SendMailAsyncResult.End(IAsyncResult result)
at System.Net.Mail.SmtpClient.SendMailCallback(IAsyncResult result)
collationlevel : 0
modifiedon : 4/26/2018 12:09:59 PM
tracecode : 28
errortypedisplay : GeneralOutgoingEmailServerError
errordetails : ActivityId: f3ab3f14-583c-e611-80e3-5065f38b6601
>Error : System.Net.Mail.SmtpException: The server committed a protocol violation The server response was:
at System.Net.Mail.SendMailAsyncResult.End(IAsyncResult result)
at System.Net.Mail.SmtpClient.SendMailCallback(IAsyncResult result)
collationlevel : 0
modifiedon : 4/26/2018 12:09:59 PM
tracecode : 28
errortypedisplay : GeneralOutgoingEmailServerError
errordetails : ActivityId: f3ab3f14-583c-e611-80e3-5065f38b6601
>Error : System.Net.Mail.SmtpException: The server committed a protocol violation The server response was:
at System.Net.Mail.SendMailAsyncResult.End(IAsyncResult result)
at System.Net.Mail.SmtpClient.SendMailCallback(IAsyncResult result)
collationlevel : 0
modifiedon : 4/26/2018 12:09:59 PM
tracecode : 28
errortypedisplay : GeneralOutgoingEmailServerError
errordetails : ActivityId: f3ab3f14-583c-e611-80e3-5065f38b6601
>Error : System.Net.Mail.SmtpException: The server committed a protocol violation The server response was:
at System.Net.Mail.SendMailAsyncResult.End(IAsyncResult result)
at System.Net.Mail.SmtpClient.SendMailCallback(IAsyncResult result)
collationlevel : 0
modifiedon : 4/26/2018 12:09:59 PM
tracecode : 28
errortypedisplay : GeneralOutgoingEmailServerError
errordetails : ActivityId: f3ab3f14-583c-e611-80e3-5065f38b6601
>Error : System.Net.Mail.SmtpException: The server committed a protocol violation The server response was:
at System.Net.Mail.SendMailAsyncResult.End(IAsyncResult result)
at System.Net.Mail.SmtpClient.SendMailCallback(IAsyncResult result)
collationlevel : 0
modifiedon : 4/26/2018 12:09:59 PM
tracecode : 28
errortypedisplay : GeneralOutgoingEmailServerError
errordetails : ActivityId: f3ab3f14-583c-e611-80e3-5065f38b6601
>Error : System.Net.Mail.SmtpException: The server committed a protocol violation The server response was:
at System.Net.Mail.SendMailAsyncResult.End(IAsyncResult result)
at System.Net.Mail.SmtpClient.SendMailCallback(IAsyncResult result)
collationlevel : 0
modifiedon : 4/26/2018 12:09:59 PM
tracecode : 28
errortypedisplay : GeneralOutgoingEmailServerError
errordetails : ActivityId: f3ab3f14-583c-e611-80e3-5065f38b6601
>Error : System.Net.Mail.SmtpException: The server committed a protocol violation The server response was:
at System.Net.Mail.SendMailAsyncResult.End(IAsyncResult result)
at System.Net.Mail.SmtpClient.SendMailCallback(IAsyncResult result)
collationlevel : 0
modifiedon : 4/26/2018 12:09:59 PM