Which transactional SMTP providers offer granular control over sending volume and speed per ISP?

Email marketer from Twilio SendGrid Help Center explains that SendGrid doesn't allow direct ISP-level throttling. However, features like IP management, dedicated IPs, and segmentation enable senders to optimize deliverability which could indirectly affect sending to specific ISPs.

Email marketer from SocketLabs explains that you can configure custom processing/routing rules using their Rule Engine (available on enterprise-tier service plans)

Email marketer from SparkPost Help Center explains that SparkPost provides features for managing sending reputation but doesn't expose explicit ISP-level controls. Users can leverage segmentation and engagement data to optimize sending patterns, which can help manage deliverability to specific ISPs.

Marketer from Email Geeks shares that controlling sending volume/speed is possible upstream of the API, using auto-warmup for a dedicated IP (applies to all traffic, not per domain). Ongage offers throttling/diversion due to its interface with multiple SMTP APIs.

Marketer from Email Geeks explains that to granularly control sending volume and speed per ISP, you'll need to run your own server, as SaaS providers typically manage deliverability.

Email marketer from Amazon SES Documentation explains that you can request increases to your sending limits, but it does not provide specific options for throttling to individual ISPs. You could use configuration sets with different dedicated IPs to segment sending, but this would still be an indirect method.

Email marketer from Stack Overflow recommends building a custom SMTP server setup using Postfix or Exim, allowing full control over sending parameters, including ISP-specific rate limiting, but notes the complexity of managing reputation and infrastructure.

Marketer from Email Geeks shares that they've been able to make changes to sending configurations in GreenArrow’s cloud MTA.

Email marketer from GreenArrow states their cloud MTA can allow modifications for sending configurations, which would include control over sending volume and ISP

Marketer from Email Geeks mentions that SocketLabs allows custom processing/routing rules via their Rule Engine (enterprise tier). Suggests exploring SES Mail Manager for similar custom policy features.

Email marketer from Email Marketing Forum notes that smaller, lesser-known SMTP providers might offer more flexibility in custom configurations, including ISP-level controls, but suggests carefully evaluating their reliability and reputation.

Email marketer from Mailgun Help Center explains that while Mailgun doesn't directly offer ISP-specific sending volume control, it provides tools like IP Pools and Routing Rules to manage sending reputation and delivery based on different criteria, indirectly influencing ISP-level delivery.

Email marketer from Reddit suggests PowerMTA or a similar on-premise solution for granular control over sending volume and speed per ISP, noting that most SaaS providers restrict this level of access.

Expert from Word to the Wise explains that while some ESPs may offer certain levels of customization, direct control over sending volume and speed per ISP is generally limited. She recommends carefully evaluating the specific needs and technical capabilities before choosing an ESP.

Expert from Word to the Wise suggests that building your own custom solution, possibly leveraging open-source MTAs or a hybrid approach, provides the highest degree of control over sending volume and speed per ISP but requires significant technical expertise and resources.

Documentation from PowerMTA explains that PowerMTA allows configuring delivery settings at the domain or IP level, which can be used to implement ISP-specific throttling. It supports flexible configuration for managing sending rates and concurrency based on various parameters.

Documentation from Exim details how to configure rate limiting and concurrency settings. Exim's flexible configuration enables defining different sending rates per domain or IP, allowing for ISP-specific settings, though this requires manual configuration.

Documentation from Postfix outlines the use of transport maps for directing mail to different delivery transports, combined with rate limiting features, enabling a custom solution for managing sending volume to different ISPs. Configuration requires advanced knowledge of Postfix.