No one is fond of receiving e-mails you haven't asked for, so called unsolicited e-mails, or spam.
If you contact private individuals in this way, it is even against certain laws (most notably the US CAN-SPAM Act of 2003).
When is it legitimate to send e-mails to many, then?
Sometimes you do need to send e-mails also to people you haven't contacted before, and if you do it to representatives of companies, you are generally allowed to, and if you just send an e-mail from one person to another, no one thinks this is very strange.
However, sometimes you even want to contact a large group of people with a similar request in a legitimate way, but how do you do that in a way that will be read and responded to, when peole so easily will judge your e-mail as being spam?
This is where you need a tool:
- which will not classify you as spam,
- which will allow you to insert customized variables to make it personal,
- which will need to be sendable from your own company e-mail domain and not some obscure spam-looking e-mail address or public-domain e-mail address such as gmail, hotmail, yahoo and the like,
- which will allow you to set the exact time, when your e-mails need to go out,
- which will allow you to send e-mails in the way humans and not machines do, like only during office-hours, and
- which will allow you to send your e-mails in a whatever pace feels most comfortable to you such that you would have time to respond to responses.
Now, we may be partial, but we don't know of any other tool than Otto (see ordering and price info here) that can do all of these things.
You can read about how it will not be treated as spam here, how you can insert variables here, how you can send from your own e-mail domain here, and the last three bullets are more explained in this article:
How to send e-mails at a specific time?
This is probably something that most newsletter services will help you do, but it gets a little trickier from your normal e-mail tool, like Outlook.
If you want to make sure that you want to send something directly related to International Women's Day, March 8th, e.g., but you know that you won't be able to press the send-button at the right time, then settings such as these will help you:
How to send e-mails to many without getting swamped with replies all at the same time?
The best way of actually getting a response is NOT to ask the user to click on a link, but to encourage the person to call you, or to e-mail you back.
Actually, there is just one little character that will boost response rates 3-4 times... It's simply the question-mark (?)! Keeping your e-mail short and personal will help, too, but it becomes even better with just one question that the recipient will know the answer to. (And it gets even better if it's the answer to a question that the recipient feels a little proud he knows the answer to, too 
)
However, as soon as you have many, say 50 and upwards, on your recipient list, it quickly gets quite tricky to be able to handle answering up to all those people coming back to you at just about the same time if you don't have a way to pace or throttle the e-mails going out. In Otto, you can set that pace.
How to send e-mails to many during office-hours only
If you now know that you can set a specific pace, you probably don't want it to keep on sending throughout nights and weekends. It would make it tougher to handle Monday Mornings, and it simply doesn't look very professional either, and to be honest: Anyone will think you've used the help of a machine to do it, or that you are one yourself being up working in the middle of the night...
In Otto, you can set whether if e-mails should go out also after office hours on weekends with it's two settings:
Final words on sending to many
If you need to comply with the CAN-SPAM Act referenced above, you need to include both your physical address, complete legal name, and an unsubscribe link, all of which you naturally can do also with Otto.
