Connect will only allow a maximum of 20 emails at one time to avoid your IP being placed on a blacklist, please read the below to find out more about what these are;
Some email servers and spam filters reference "blackhole lists," which are lists of IP addresses of known spammers, or "spam friendly" servers. If an IP address is on the list, they won't let your email through. You can be placed on this list either from multiple recipients flagging your emails as spam or by your ISP if they notice your server is sending out a large number of emails in one go.
Anyone can setup a blacklist for their own email server, and share the list for the public to use. Most large ISPs only use the most reputable blacklists like SpamCop, Spamhaus and URIBL.
If a server gets on a blacklist such as SpamCop, any email from the server is blocked by ISPs that use the SpamCop blacklist. SpamCop and other reputable blacklists usually have a threshold, and usually delist servers after a reasonable period of time.
Find out if your IP address is on a blackhole list at http://multirbl.valli.org/lookup/.