SndLatr nicely integrates with the Gmail user interface, so there is no need to leave Gmail.
Schedule mails to be sent later
SndLatr adds an additional Send Later button. This button brings up a drop-down where you enter human readable dates like "Friday on 9 am" or "1st of next month, 11 am". You can also pick a date with using a regular date picker.
A scheduled email remains in the Drafts folder while it has not been sent yet and can be edited or deleted like any other mail. If it is deleted from the Drafts folder, it will not be sent. It can also be cancelled, if do not want it to be be sent automatically anymore but want to keep it as a draft.
Replies can be scheduled in the same way:
Setting up reminders
SndLatr adds a new button to conversations, that allows to set up reminders. Reminders can be used to bring conversations back to your inbox at a later date. This is a nice tool to keep your inbox clean. Just archive the conversation after setting up a reminder and it will be back in your inbox when you need to deal with it.
How does it work?
SndLatr works by injecting additional Buttons etc. into the Gmail web interface. When a mail is scheduled or a reminder is set up, it sends metadata about the message (the message id and the date) to a back-end (server). The message itself remains stored at Gmail. In due time, the back-end fetches the message from Gmail and sends it. When a message has been sent, it appears in the Sent folder and is removed from the Drafts folder