If you're sending emails by syncing your Outlook or Gmail account, this will improve your delivery rates and overall success. However, keep in mind that both Gmail and Outlook impose a limit on how many emails can be sent by 3rd party apps like BuzzBuilder.
Gmail Users:
If you're sending via your personal Gmail account, Gmail's servers will allow you to send 100 emails per day via 3rd party apps like BuzzBuilder. If you have a Google Work (G-Suite) account, this will usually allow up to 2000 emails per day. However, if you're using a Trial version of G-suite, it will limit you to 500 per day. Click here for more information about gmail sending limits.
Outlook Users:
If you're sending via your Outlook Exchange or 365 account, you're generally allowed 1000 emails per day, but this could vary depending on your specific Outlook server. Some hosting companies will only allow 400. Godaddy hosting allows 1000 and this is a recommended resource to use. Some hosting companies such as Quest do not allow you to send any emails via 3rd party apps (such as BuzzBuilder). Be sure to check with your email provider and ask about the email limits they impose--be sure to let them know that you're using an email application that will relay emails via your Outlook account.
NOTE: Keep in mind that these email limits include emails being sent from new campaigns as well as emails sent from campaigns in progress. For example, imagine you sent a drip campaign to 200 contacts last week on Monday and email 2 from the campaign is scheduled to send the following Monday. This means on the following Monday there will be 200 emails delivered. However, if you also launch a new campaign on the same Monday to a new list of 150 contacts, then there will be a total of 350 emails being sent (200 from last week's campaign in progress + 150 from this week's launch). If you're sending via a personal Gmail account and are limited to 300 emails per day, you would now be over that limit.
You also need to consider whether you're exceeding your allowed Contact Credits
Your BuzzBuilder license allows you to store a certain number of contacts in the database (normally 2500). Even though your Outlook or Gmail account might allow you to send more emails, if you've reached your limit for the number of contacts allowed, then it will alert you that the file being imported will exceed this.