If you use services like gmail or office365 the problem usually is that they have lots of restrictions. You can send one off emails no problem and that'll work fine. But if you send things in bulk you're likely to get rejected at some unpredictable point.

These days using ISP email addresses for any sort of bulk sending or even for sending messages as part of a Web application that sends frequent messages, chances are you will get blocked.

Nor is that a good idea at least with an account you care about as it's likely to get flagged as Spam. For scenarios that require more than one off sending I'd always recommend using a mail service like MailGun, MailChimp, SendGrid or Trello which provide more reliable sending for one, and are set up to allow for bulk sending. Many of these type of services have some free tiers that are often enough for sending small bulk or Web site based messages for free or low charges and can scale up to large volumes - they can also automate bulk sending via APIs so you can send a message and recipient list and they'll do the sending for you.

I use MailGun with their free tier (which changes frequently) and I get 10,000 messages a month for free with (reasonable) charges for anything over that in increments of a thouand. MailChimp is similar I believe. I very rarely go over the limit (usually when there some problem with attempted hacks or log errors).

Another reason to use services like this too is that they handling logging and tracking so if messages don't go through you can often find out where it went wrong with more info. This is hard to do with an SMTP only solution you do on your own (you can only track direct send errors that way).

+++ Rick ---

>Hi,
>
>A couple of my customers use the email server smtp.office365.com. Prior to this, I have never come across this type of the SMTP server.
>I have a couple of questions:
>1. Is smtp.office365.com an online email server that MS offers for $$?
>2. I have a Family edition of the Office 365. Do you know if I could use an online SMTP smtp.office365.com or you need to purchase a different subscription?
>
>Basically, I am thinking that if I could use such an online SMTP (if my assumption is correct), I could resolve some issues that the customers come across.
>
>TIA