How do I synch all emails on all devices?

kraut55 wrote:

In my Mail app I have 3 mail accounts. One is my main account xx@hotmail.com, the second one is xx@gmail.com and the third is my icloud account. It has happened several times that I had sent a message from one device i.e. my iPad. When I later tried to find it but did not remember that I had used my iPad I had to check on iPhone, MacBook etc. to finally find it on my iPad. What settings do I have to change to have all messages on all devices?

Emails do not sync between devices.

Each device syncs to the email client server using the internet. Thus if one device is not connected to the internet it may not sync with the client-server and will not refresh with the actions taken on the other devices. They need not be on the same WiFi.

kraut55 wrote:

Another question, maybe related: I am looking for an email of a certain address. When I enter it in the search box I get x answers. I click on all recipients that are shown but the message I am looking for is not there. When I enter a very specific word in the search box from the email the message suddenly shows up in exactly the same recipients address I had searched for before. ??

What I have experienced is when you keep using the iPhone regularly the contacts and eamil IDs with whom you interact are learn by your device and are displayed.