An error occurred...

Keep Getting Synchronizing folder ‘XXXXXmail/calendar/’ failed due to the following error: The remote server returned an error:(503) Server Unavailable.
Why am I getting this all the time?

Yeah I’m getting it too on my account.  Using eM Client version 7.0.26356.0

I was getting that message all the time with version 6.  The beta version seemed to solve it for a while.

My Android phone can sync that calendar just fine right now so I don’t think its MS fault.

I got an email from MS saying

“It appears that you are currently using the Windows Live Mail 2012 application to connect to your Outlo‍ok‍.‍com account. The Windows Live Mail 2012 application does not support the synchronisation technologies used by the new Outlo‍ok‍.‍com.”


Please take action before 30 June 2016, which is when we’ll begin upgrading accounts that currently use the Windows Live Mail 2012 application.

The only things I have connected to this account are my android phone (version 6.0.1), The Windows 10 Mail app (it just does it automatically because I log into my Windows profile with that account. and eM Client.  and eM client is the only thing complaining.

Here’s what’s in the log

11:15:17 AM   [hidden] [AirSync]  Synchronizing folder '[hidden]’s calendar/'11:15:20 AM    MailClient.Storage.Application.OperationException: Synchronizing folder ‘[hidden]’s calendar/’ failed due to the following error: The remote server returned an error: (503) Server Unavailable. —> System.Net.WebException: The remote server returned an error: (503) Server Unavailable.
11:15:20 AM    at System.Net.HttpWebRequest.EndGetResponse(IAsyncResult asyncResult)
11:15:20 AM    at MailClient.Protocols.AirSync.Protocol.ActiveSyncCommandRequest.GetResponse(CancellationToken cancellationToken)
11:15:20 AM    at MailClient.Protocols.AirSync.AirSyncItemSynchronizer2.Synchronize(IItemSynchronizeContext1 synchronizeContext, Folder folder, CancellationToken cancellationToken)
11:15:20 AM    at MailClient.Protocols.Common.ItemSynchronizer`2.<>c__DisplayClass28_0.b__1(WorkerStatus status, CancellationToken cancellationToken)
11:15:20 AM at MailClient.Protocols.AirSync.AirSyncGenericCommand.Execute(WorkerStatus status)
11:15:20 AM — End of inner exception stack trace —
11:15:20 AM at MailClient.Protocols.AirSync.AirSyncGenericCommand.Execute(WorkerStatus status)
11:15:20 AM at MailClient.Commands.Command.Process(WorkerStatus status)

Sorry for the wrapping, the ‘pre’ tag just truncates the lines on this page.

It just synced the calendar.  If its just a connectivity issue, then perhaps eM needs to be less verbose about it.  I’m sick of it popping up all the time complaining about sync issues.

if this issue happens with a hotmail/outlook account the issue is most likely the fact that Microsoft is currently migrating its mail accounts to Exchange and the previously used AirSync protocol is discontinued.
Unfortunately a solution to this is to set up your account anew as Exchange or IMAP.


Hi Olivea,
It seems by unclicking AirSync stops (503) Server Unavailable error message.
At least working for me last 24 hours.

Yeah but your calendar can’t sync without AirSync.  and Olivia makes it sound like soon with the changes MS are making, it won’t sync at all.  I can’t connect my as an exchange account, so I don’t know what’s going to happen.

For the time being I’ve turned off Show Operations Window when an error occurs.  That way it syncs the calendar when it can, and doesn’t bother me when it can’t

Microsoft is migrating ALL its accounts to Exchnage and claim to be done by August.
When your account is available, you will be able to set it up as Exchange in eM Client.