Limits for Assignment, Auto-Response, and Escalation Rules Salesforce limits the number of rules, as well as the number of entries and actions per rule. These limits apply to assignment rules, auto-response rules, and escalation rules. LIMITVALUETotal rules across objects (Applies to any combination of workflow, assignment, auto-response, and escalation rules,active and inactive.)2,000 Active rules per object (Applies to any combination of active workflow, assignment, auto-response, and escalation rules, as well as record change processes.)50 Total rules per object (Applies to any combination of workflow, assignment, auto-response, and escalation rules, active and inactive.)500 Entries per rule3,000 Formula criteria entries per rule300 Filter criteria per rule entry25 Actions allowed per rule200
As per my understanding of your question, I dont think there's any email limit on emails sent via Auto-response rules or case assignment rules.
There is no limit on sending individual emails to Contacts, Leads, Person Accounts, and Users from your org directly from Account, Contact, Lead, Opportunity, Case, Campaign, or custom object pages. Salesforce does not count single emails sent using the email author or composer.
Salesforce limits the number of rules, as well as the number of entries and actions per rule. These limits apply to assignment rules, auto-response rules, and escalation rules.
LIMITVALUETotal rules across objects
(Applies to any combination of workflow, assignment, auto-response, and escalation rules,active and inactive.)2,000
Active rules per object
(Applies to any combination of active workflow, assignment, auto-response, and escalation rules, as well as record change processes.)50
Total rules per object
(Applies to any combination of workflow, assignment, auto-response, and escalation rules, active and inactive.)500
Entries per rule3,000
Formula criteria entries per rule300
Filter criteria per rule entry25
Actions allowed per rule200
Refer this links
https://help.salesforce.com/articleView?id=rules_limits.htm&type=5
There is no limit on sending individual emails to Contacts, Leads, Person Accounts, and Users from your org directly from Account, Contact, Lead, Opportunity, Case, Campaign, or custom object pages. Salesforce does not count single emails sent using the email author or composer.
"https://help.salesforce.com/articleView?id=000271357&language=en_US&type=1"
However, check this with salesforce, Tweet #asksalesforce - they'll give you a perfect answer