This is not done because your ISP is mean or trying to pull a fast one, it is to ensure that the mail server will be available to support all its users and to prevent spam from being sent through their system.
If you exceed your hourly or daily email limits, you will notice errors being returned after the quota is met. Common errors messages look like this:
You have reached your daily sending quota…
This can create a problem for your business as once you have exceeded your SMTP email sending, you will generally have to wait 24 hours before you can send more email through that server. It is important to note that this period is not clock dependant and is set at 24 linear hours – so you cannot send a batch of emails at 23:55 and then again at 00:05, your quota would only be reset at 23:56 the next day.
The Chameleon-i Guide to Email – Want to know how Chameleon-i sends and receives email click here.
Below is a list of some of the larger ISPs and their mail server limits, this is not exhaustive, and you should verify your limits with your ISP.
Exchange – Office 365
Sending limits across Office 365 options
– 1 message every minute with a 10-second pause between messages.
1and1 Help Centre
The email server limits senders to send only 250 outgoing emails per day, but you can send more email by adding SMTP relays to your GoDaddy account
– 500 emails per day when sending from their web interface
– 100 emails per day when sending from a desktop email client
– 10mb per message
Gmail email sending guidelines
Windows Live Hotmail
– 100 emails per day
– 10mb per message
Windows Live Hotmail email sending guidelines
Yahoo – • Yahoo Mail – Email Send Rate Limits & Other Email Restrictions
The following restrictions apply when sending emails from a Yahoo Mail account:
– Yahoo Mail email send limit – no more than 100 emails or recipients per hour
– Yahoo Mail other SMTP limits – max 10Mb per message for the free Yahoo Mail Service, or 20Mb per message for Yahoo! Mail Plus
– Yahoo! Anti-Spam Policy – http://docs.yahoo.com/info/guidelines/spam.html
– Yahoo Mail SMTP restriction expiry method – N/A
It is worth noting that on top of a daily send cap, for security reasons, all email service providers also limit the maximum size email and attachment that an email account can receive.
25Mb (per email sent or received)
Outlook.com and Hotmail
10Mb (per file attachment) or 300Gb (only for files attached via SkyDrive!)
25Mb (per email) or unlimited (only for files attached via DropBox – limited by your DropBox account size)
12Mb (per email) and 10Mb (per file)
30Mb (per email) and 20Mb (per file)
20Mb (per attachment)
Windows Live Mail
10Gb (per email) and no more than 50Mb per file attached
If the hourly or daily email sending limits of your outgoing SMTP mail server do not support the size of your mailing list or the frequency of your email campaigns, there are options to send more email each day, such as using a secondary SMTP mail server relay or email software with an internal SMTP engine. You can also contact your ISP and ask if they are able to increase your daily limit. (There may be an additional charge for this.)