IP Address

The common understanding of an IP address, this presents as four groups of up to three decimal digits, each separated with a dot. This creates a 32-bit number.

You can express IPv4 address ranges in Classless Inter-Domain Routing (CIDR) notation. IPv4 CIDR notation presents as an IP address followed with a forward slash and one decimal integer. This integer, the block, counts the number of consecutive leading 1 bits in the network mask. This limits the range to a certain number of IP addresses.

192.0.2.130/32 = 192.0.2.130

Interpret this as the IP address 192.0.2.130 with a network mask of 32 consecutive number 1, or 255.255.255.255. This masks out all other IP addresses but itself, a single internet host.

192.0.2.130/31 = 192.0.2.130, 192.0.2.131

Interpret this as the IP address 192.0.2.130 with a network mask of 31 consecutive number 1, or 255.255.255.254. This masks out all other IP addresses but itself and one other IP address.

Introduced to fix the limited address space of IPv4, IPv6 addresses contain up to eight groups of four hexadecimal digits separated with colons.

You can express IPv6 address ranges in CIDR notation as well. IPv6 CIDR notation presents as an IP address followed with a forward slash and one decimal integer equal to the prefix size in bits.

Sent emails include IP addresses in the headers. These IP addresses act as a return address for a given email message. Recipient inbox providers use your IP address as one of your reputation indicators.

Twilio SendGrid allows you to use a shared IP address or a dedicated IP address. If you send high volumes of email or want greater control over your reputation, use a dedicated IP address. To determines reputation of senders on shared IP addresses, inbox providers use the performance of all the senders sharing that IP address.

• SendGrid Email Infrastructure Guide
• Configure Reverse DNS