Blackbaud's Role in Email Delivery

As an ESP, Blackbaud's sending system is robust and scales well for clients both large and small. Since our system can send large numbers of messages simultaneously, we conform to standards for high-volume senders to ensure email delivery.

When you send an email, your application — such as Luminate Online or Blackbaud NetCommunity — sends information and email content via web services to Blackbaud's servers. To process the messages, our servers:

  • Validate email formats

  • Remove addresses that meet suppression criteria

  • Merge the remaining recipients' information and other merge fields with the content

The servers then send the processed messages to our Mail Transfer Agent (MTA) servers, which physically transmit messages using SMTP protocol to mailbox providers through multiple shared Internet protocol (IP) addresses. These servers can send millions of email messages per hour on even the heaviest of email volume days — such as Giving Tuesday and End of Year — and include configurations to automatically respond to the various tools and algorithms mailbox providers use to track and block senders who don't follow industry best practices.

We use this system in combination with a dedicated team of email specialists to help ensure your messages reach their intended recipients.


Whitelists are lists of approved senders that mailbox providers maintain to recognize cooperative senders when they receive messages in large quantities.

Our email specialists coordinate and maintain our statuses on these lists across the major mailbox providers that use them to help increase the:

  • Likelihood that messages reach their recipients

  • Number and speed of emails we can send to them without triggering their SPAM filters

  • Number of emails we can send to them before they return messages as "undeliverable" because they received too many messages at one time


SPAM blacklists are domain and IP address inventories of senders with poor reputations which sometimes help mailbox providers determine whether to place messages in recipient inboxes. Large trustworthy companies, as well as small, independent networks, create these lists and each provider uses them differently.

Typically, mailbox providers combine data from various public blacklists — as well as information from their own networks — to determine the credibility of a sender. Subsequently, many lists have little to no effect on IP reputation. Major providers disregard low-priority lists entirely and only use information from high-priority services such as SpamHaus and SpamCop.

Blackbaud subscribes to ReturnPath — the email industry’s leading deliverability solution provider — to monitor external blacklists for our IP addresses. When necessary — such as on the rare occasions when SpamHaus or SpamCop list our IP addresses — our team of email specialists immediately request to delist them. We recommend you use services such as to monitor your domain and, if necessary, request to de-list it.

Note: Blacklist companies don’t block messages. Rather, mailbox providers use the listings as reasons for blocks. To prevent blocking, we recommend you manage your list quality and maintain a database of engaged recipients.

Suppression lists

To maintain favorable reputations with mailbox providers, our system reviews recipient lists and automatically suppresses email addresses for the following reasons:

  • Hard bounces — When email delivery fails, mailbox providers send bounce code responses. The system categorizes and tracks these bounce codes so that it can suppress email addresses when they fail, such as when a recipient's address is invalid or their account is closed.

  • SPAM complaints — Our email specialists help maintain Feedback Loop (FBL) agreements with mailbox providers that offer FBL programs. With an FBL agreement, a mailbox provider agrees to inform us when a recipient marks a message as unsolicited — such as when they select a "This is SPAM" button or link — so that our system can suppress their email address from future mailings from that sender.

    Note: If the same email address appears in the recipient list for a mailing from another Blackbaud client, our system does not suppress it unless the recipient also marks the message from the other client as unsolicited.


  • Opt-out links — When a recipient uses a legally required opt-out link in a message to request removal from emails, our system suppresses their address from future mailings specific to their request, such as only for a particular newsletter or all emails from an organization.


  • List unsubscribe links — If you send from Luminate Online, the system supports unsubscribe requests from links that some mailbox providers — including Gmail and Outlook Mail — add to the top of messages. When recipients select these links rather than report your message as SPAM, there's no negative impact to your sender reputation with the mailbox provider.

    Note: While the unsubscribe link that appears at the top of messages is a more trusted and convenient option for recipients, current email laws still require organizations to include an unsubscribe link — as well as their physical mailing address — within the content of bulk email.


Some mailbox providers return messages as “undeliverable” or delay their delivery if an ESP tries to send too many emails at one time.

To avoid returned or delayed messages, our system uses a process known as throttling to restrict the number of concurrent connections it makes with mailbox providers to comply with their threshold specifications. Our email specialists continually monitor throttling limits and adjust our send rates as necessary — or as required — to ensure email performance.

Shared IP addresses

Mailbox providers evaluate the reputations of our system's individual IP addresses when they determine message deliverability. An IP address' reputation is the result of factors such as how frequently it sends messages and whether content engages recipients.

To help support positive sender reputations, our system enables clients to share IP addresses. When multiple clients use an IP address, they leverage the benefit of increased sending volume.

The system also dynamically shifts senders between IPs as necessary to:

  • Optimize delivery

  • Prevent mailing practices of individual organizations from adversely impacting an IP's reputation for others

  • Help maintain email volume through each IP

Note: Blackbaud uses separate shared IPs and MTAs for other lower volume email types such as autoresponders, notifications, and constituent-originated messages.

IP designation

If you use Luminate Online to send email, you are likely a high volume sender. To protect overall deliverability, the system calculates a SPAM complaint rate for you — based on information it receives from mailbox providers — and assigns you a grade to determine which IP addresses to send your mailings from.

To calculate the rate, the system counts how many complaints it received about your messages over the past 30 days and divides the number by how many emails you sent. The system updates the rate each night and uses the current average to assign your grade whenever you send a message.

When you manage the quality of your recipient lists and follow other deliverability recommendations, you are more likely to receive fewer SPAM complaints. A low SPAM complaint rate allows the system to assign you to IP addresses with higher reputations.

Note: Each quarter, our email specialists review how many messages the IP addresses send on average and adjust the SPAM complaint rate threshold for each grade as necessary. These changes help ensure our IP addresses share volume equally and send messages efficiently.

Note: Manual changes to sender grades are not supported because our system overrides updates as part of its automatic process.

Our email specialists closely monitor email practices and, if necessary, can intervene to disable service for a sender if they violate the Acceptable Use Policy and disrupt delivery for others.