Can I silence only certain notifications during the night? I would like to be able to set up a silent period (at night for sleeping) where email alerts - but ONLY email alerts - will be silenced. 

I still would like to have text messages and phone rings be normal. 

Is there any way to do this automatically, without needing to go into the email app every night and turn off notifications and then remember to turn them back on in the morning?
If you do not depend on a data connection, there may be some solutions around: The Google Playstore has a lot of automation apps to offer, which you can use to set up more than this. In your case, this would be a time-based scenario:

From 11pm to 7am, disable WiFi and mobile data

No data connection => no new mail => no new mail notifications. Apps capable of things like that include e.g. Timeriffic (free, and one of the top-apps in this section), Llama (also capable of location-based and other rules), and -- my favorite -- Tasker. Though the latter is not the cheapest one, it is the most flexible, and you can get a 7-day-trial at their homepage.

For examples what else you can achieve with Tasker, you might also want to take a look at What is Cell standby and how can I keep it from eating my battery?, and the examples at the mentioned homepage. Also, a Google search on Tasker profiles will list you a lot of goodies.

To accomplish your goal using Tasker, simply create the following profile:

Context:


Time (fill in your "from" and "to" to define the time frame)


Task:


Net->Mobile Data: Set Off
Net->WiFi: Set Off


That's all. Say you defined it as described above (11pm to 7am), Tasker would switch off WiFi and Mobile Data at 11pm, and return to the previous state at 7am.

More solutions can probably be found here: Is it possible to only silence certain notifications?