I want to send out a marketing email to a little over 11,000 email addrresses using Outlook 2007 (could also be 2010) on an account configured to use the SendGrid SMTP server. what is the limit to the number of email adresses I can put into the BCC field before sendgrid will start complaining? Can I put all of them in there, or do I need to process them in batches? How big can the batches be?
from sendgrids documentation
Customers should utilize SMTPAPI if this is an option. As with SMTP, 100 messages can be sent with each connection, but there can be 1000 recipients for each message.
reminding that the receiving end also has limits on how many mail addresses you can put on the to , cc and bcc fields