I have a Xeams mail server running on Synology NAS. I found out that if I try to use same account on two or more different devices connect to the server through SSL connection then my IP will be blocked, I can see it in InvalidPasswordAttempts.log What's going on here? Right now I can only 1. restart server 2. remove ip from blocked list 3. wait for 10 min  Is there any other solutions can allow me to use one account on multiple devices. All above test are done in Apple mail and Iphone IOS mail.

David,

Here are some of the reasons for an IP to get blocked:

• The email client is configured to use an incorrect password
• The email client is trying to figure out/guess settings on the server, which causes many invalid requests. These invalid requests can be mistreated as an attack, which will cause the IP to get blocked.

Go to Server Configuration/Manager Alerts and increase the alert threshold to a higher value, such as 50.

Thanks for reply.

I am not quite understand your second point here. Client is trying to figure out/guess settings on server? Do you mean client mail app will self adjust the settings to fit mail server by making multiple requests?

In my case if I only use client mail app on my mac laptop then my IP is not blocked only when I start using mail app on my Iphone then IP will be blocked. I have done some research on this problem and found there seems have similar issue but it was happen with POP3. https://www.xeams.com/iphonepop.htm I am using IMAP instead of POP3 here. Do Xeams mail server allow multiple devices use same account to connect to mail server at same time?

But here I will try out your suggestion to raise threshold and test. 

David,

Yes. Often, clients try to guess the parameters and send invalid values to see what works.

The only explanation for your symptoms is that you have specified incorrect values on your iPhone. Note that it is not just your password. If a client connects to an SSL port but sends unencrypted messages, Xeams may misinterpret that as an attack.

The IMAP protocol supports simultaneous access, so you should be able to connect from both your MAC and iPhone. We do this all the time.

Ok I have tried the method you suggested by increase threshold to higher number and it work.

By the way. During the testing I notice that client mail app seems a bit of delay for receiving mail. Although I can change Check for new messages option to Every minute on my Mac. I assume this only have to do with client app nothing have to configure on Xeams. Am I right?

Another thing is push notification. When I sent a mail from Gmail to Xeams mail box notification for mail did not show up on my IOS. Do you no how to make it work?