A rather interesting solution has appeared in Cydia for everyone who actively uses the mail client on iOS devices and deals with a large number of letters. The authors of the Check tweak were inspired by the ability to select multiple objects, which is implemented in Windows using the Shift key.
They did not add extra buttons to iOS, but they implemented the ability to quickly select several letters from the list.
After installing the tweak Check does not add icons and menu bars in the settings. It works very simply. When you need to perform the same action with several letters, for example, delete or move them, there is no need to select each of them. Now you just need to select the first in the list and hold your finger on it. The highlight will blink, it means that the group selection mode has been activated. After that, just click on the last letter and the entire list will be selected. Thus, you can not only mark, but also deselect the letters.
The Check tweak has already appeared in Cydia and is completely free.